CUET UG Applied Mathematics Booster Test 2 - Congruence Modulo and Equivalence Classes
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QUESTION 1 OF 20
Evaluate whether a ≡ b (mod m) holds true if a = 31, b = 21, and m = 5. Which foundational check confirms this?
QUESTION 2 OF 20
Match List 1 with List 2.
| List 1 | List 2 |
|---|---|
| 1. a = 41, b = 21, m = 5 | a. a ≡ b (mod 9) is perfectly valid |
| 2. a = 31, b = 21, m = 5 | b. a ≡ b (mod 5) leaves remainder 1 |
| 3. a = 15, b = 6, m = 9 | c. a ≡ b (mod 6) is perfectly valid |
| 4. a = 14, b = 8, m = 6 | d. a ≡ b (mod 5) leaves remainder 1 |
QUESTION 3 OF 20
If two positive integers a and b leave the same remainder r when divided by a positive integer m (where a = ms + r and b = mt + r), which of the following deductions are correct?
1. a - b = m(s - t)
2. m divides (a - b)
3. a ≡ b (mod m)
4. a mod m ≠ b mod m
QUESTION 4 OF 20
Consider the congruence 41 ≡ 21 (mod 5). Identify the incorrect statement regarding its verification:
QUESTION 5 OF 20
When segregating the first 50 positive integers into sectors for modulo 6, the mixture of elements in sector 1 (remainder 1) includes which of the following?
QUESTION 6 OF 20
In a Modulo 6 cyclic wheel, the numbers belonging to the same subset (sector) leave the same remainder. What is the constraint region for the total number of distinct subsets formed?
QUESTION 7 OF 20
In the definition of equivalence class [X] = {a ∈ Z | a ≡ X (mod m)}, what is the set of elements if m = 3 and X = 1?
QUESTION 8 OF 20
Moving through the sequence of modulo 3 equivalence classes, which class contains the number 11?
QUESTION 9 OF 20
To prove the symmetric property Rm, if a ≡ b (mod m), it strictly implies b ≡ a (mod m). What is the probability that this property fails for any integers 'a' and 'b' that already satisfy the premise?
QUESTION 10 OF 20
In establishing the reflexive property, vectorially calculating m | (a - a) yields 0. What does this mean for the relation a ≡ a (mod m)?
QUESTION 11 OF 20
Suppose a ≡ b (mod m) and b ≡ c (mod m). By substituting b = a + km and c = b + k'm, the calculated area of difference (c - a) is equal to:
QUESTION 12 OF 20
The relation Rm defined by a Rm b if and only if a ≡ b (mod m) is an equivalence relation because it integrates which specific properties?
QUESTION 13 OF 20
Which statement accurately represents the fact that equivalence classes [0], [1], ..., [m−1] for mod m are "non-overlapping sets"?
QUESTION 14 OF 20
The total number of exact equivalence classes for modulo m is represented as [0], [1], ..., up to what final class?
QUESTION 15 OF 20
Find all the positive integers strictly less than 30 forming the equivalence class of 5 for modulo 7.
QUESTION 16 OF 20
Find the positive integers less than 50 forming the equivalence class 4 for modulo 6.
QUESTION 17 OF 20
What distinguishes a Simple Arithmetic Function from a general algebraic function?
QUESTION 18 OF 20
For the arithmetic function mapping Z+ → R, if f(x) = x², what is the image if the pre-image is 5?
QUESTION 19 OF 20
If an arithmetic function machine is set to the rule f(x) = 3x + 1, and the pre-image is 4 (a positive integer), what is the generated image?
QUESTION 20 OF 20
Why are Simple Arithmetic functions widely useful according to the passage?
Test Complete!
Answer Review
1 Evaluate whether a ≡ b (mod m) holds true if a = 31, b = 21, and m = 5. Which foundational check confirms this?
�� Congruence depends on divisibility of the difference. �� 31 − 21 = 10. �� 10 is divisible by 5.
Two integers are congruent modulo m when m divides their difference. Here, 31 − 21 = 10 and 5 divides 10 exactly. Therefore, 31 ≡ 21 (mod 5). Option A uses addition, which is irrelevant. Option C discusses parity. Option D is false because 31 and 21 leave remainder 1, not 2.
- �� Option A → Congruence is checked using difference, not sum.
- �� Option C → Odd product does not establish modular equivalence.
- �� Option D → 31 mod 5 = 1 and 21 mod 5 = 1, not 2.
Used: Substitution
Application: Compute the difference directly and test divisibility by the modulus.
Final Logic: 5 divides (31 − 21), so 31 ≡ 21 (mod 5).
"Same mod ⇒ Difference divisible."
2 Match List 1 with List 2.
| List 1 | List 2 |
|---|---|
| 1. a = 41, b = 21, m = 5 | a. a ≡ b (mod 9) is perfectly valid |
| 2. a = 31, b = 21, m = 5 | b. a ≡ b (mod 5) leaves remainder 1 |
| 3. a = 15, b = 6, m = 9 | c. a ≡ b (mod 6) is perfectly valid |
| 4. a = 14, b = 8, m = 6 | d. a ≡ b (mod 5) leaves remainder 1 |
Compare the remainders for modulo 5. Check whether the difference is divisible by the given modulus. Match each expression with the correct congruence statement.
Evaluate each pair individually. 1: 41 mod 5 = 1 and 21 mod 5 = 1. Therefore, a ≡ b (mod 5) with remainder 1. 1 → b 2: 31 mod 5 = 1 and 21 mod 5 = 1. Therefore, a ≡ b (mod 5) with remainder 1. 2 → d 3: 15 - 6 = 9, and 9 is divisible by 9. Therefore, a ≡ b (mod 9). 3 → a 4: 14 - 8 = 6, and 6 is divisible by 6. Therefore, a ≡ b (mod 6). 4 → c Thus, the correct matching is: 1 → b 2 → d 3 → a 4 → c Hence, Option A is correct.
- Option B → Incorrect because it mismatches the modulo 9 and modulo 6 congruence statements.
- Option C → Incorrect because it assigns incorrect modulo conditions to the given pairs.
- Option D → Incorrect because several congruence relationships do not satisfy the required remainder or divisibility conditions.
Used: Option Grouping
Application: Verify each congruence independently by checking either equal remainders or divisibility of the difference, and then match the complete set.
Final Logic: Only Option A correctly satisfies all four congruence relationships.
Same remainder = Same congruence class.
3 If two positive integers a and b leave the same remainder r when divided by a positive integer m (where a = ms + r and b = mt + r), which of the following deductions are correct?
1. a - b = m(s - t)
2. m divides (a - b)
3. a ≡ b (mod m)
4. a mod m ≠ b mod m
Subtract the given expressions. The difference becomes a multiple of m. Therefore, the two numbers are congruent modulo m.
Given, a = ms + r b = mt + r Subtracting, a - b = (ms + r) - (mt + r) = ms - mt = m(s - t) Therefore, Statement 1 is correct. Since a - b = m(s - t), it follows that m divides (a - b). Hence, Statement 2 is correct. By the definition of congruence, if m divides (a - b), then a ≡ b (mod m). Therefore, Statement 3 is correct. Since a and b leave the same remainder when divided by m, a mod m = b mod m. Therefore, Statement 4 is incorrect. Hence, Statements 1, 2, and 3 are correct, making Option B the correct answer.
- Option A → Incorrect because it omits Statement 3, which directly follows from Statements 1 and 2.
- Option C → Incorrect because it includes Statement 4, which contradicts the given condition of equal remainders.
- Option D → Incorrect because Statement 4 is false.
Used: Substitution
Application: Substitute the given expressions for a and b, simplify the difference, and apply the definition of congruence.
Final Logic: The difference equals a multiple of m, proving divisibility and congruence, while Statement 4 contradicts the given information.
Same remainder ⇒ Same congruence class.
4 Consider the congruence 41 ≡ 21 (mod 5). Identify the incorrect statement regarding its verification:
�� 41 ÷ 5 leaves remainder 1. �� Difference equals 20. �� Congruence is valid.
41 − 21 = 20 and 5 divides 20 exactly, so the congruence holds. Also, 21 mod 5 = 1. Since 41 mod 5 = 1, not 2, Option C is the incorrect statement. The other options correctly verify the congruence.
- �� Option A → Correct arithmetic difference.
- �� Option B → 20 is divisible by 5.
- �� Option D → 21 leaves remainder 1 upon division by 5.
Used: Elimination
Application: Verify each numerical statement directly.
Final Logic: Only Option C contradicts actual modular computation.
"41 = 40 + 1 ⇒ remainder 1."
5 When segregating the first 50 positive integers into sectors for modulo 6, the mixture of elements in sector 1 (remainder 1) includes which of the following?
�� Sector 1 means remainder 1. �� Numbers differ by 6. �� Each listed number leaves remainder 1.
Modulo 6 classes group numbers with identical remainders. Numbers 1, 7, 13, 19, and 25 all leave remainder 1 when divided by 6. Option A leaves remainder 2, Option C remainder 0, and Option D remainder 3. Hence B correctly represents sector 1.
- �� Option A → All numbers belong to remainder class 2.
- �� Option C → Multiples of 6 belong to remainder class 0.
- �� Option D → Numbers leave remainder 3.
Used: Option Grouping
Application: Check common remainder of each option set.
Final Logic: Only Option B consistently gives remainder 1.
"Sector 1 = 1 + 6k."
6 In a Modulo 6 cyclic wheel, the numbers belonging to the same subset (sector) leave the same remainder. What is the constraint region for the total number of distinct subsets formed?
�� Remainders range from 0 to 5. �� Each remainder defines one class. �� Total classes equal modulus.
For modulo 6, possible remainders are 0, 1, 2, 3, 4, and 5. Each remainder determines a distinct equivalence class. Therefore exactly six subsets exist. Options A and C provide incorrect counts, while D ignores the finite remainder structure.
- �� Option A → Excludes one valid remainder class.
- �� Option C → Adds an impossible remainder.
- �� Option D → Number of classes equals modulus, not infinity.
Used: Elimination
Application: List all possible remainders modulo 6.
Final Logic: Six possible remainders imply six subsets.
"Mod m ⇒ m classes."
7 In the definition of equivalence class [X] = {a ∈ Z | a ≡ X (mod m)}, what is the set of elements if m = 3 and X = 1?
�� Numbers must leave remainder 1 mod 3. �� Consecutive terms differ by 3. �� Option A satisfies the rule.
An equivalence class [1] modulo 3 contains all integers of the form 1 + 3k. Option A exactly matches this pattern. Option B corresponds to remainder 2, Option C to remainder 0, and Option D is merely a finite collection rather than the entire class.
- �� Option B → Represents class [2].
- �� Option C → Represents class [0].
- �� Option D → Not a complete equivalence class.
Used: Substitution
Application: Check whether numbers fit the form 1 + 3k.
Final Logic: Only Option A contains all integers congruent to 1 modulo 3.
"Class [1] = 1 + multiples of 3."
8 Moving through the sequence of modulo 3 equivalence classes, which class contains the number 11?
�� Divide 11 by 3. �� Remainder obtained is 2. �� Therefore 11 belongs to class [2].
11 = 3 × 3 + 2, so the remainder upon division by 3 is 2. Hence 11 is congruent to 2 modulo 3 and belongs to equivalence class [2]. Class [3] is not a standard modulo 3 class because valid classes are [0], [1], and [2].
- �� Option A → Requires remainder 0.
- �� Option B → Requires remainder 1.
- �� Option D → Equivalent to class [0], not distinct.
Used: Substitution
Application: Calculate 11 mod 3 directly.
Final Logic: 11 mod 3 = 2, so class [2].
"11 = 9 + 2."
9 To prove the symmetric property Rm, if a ≡ b (mod m), it strictly implies b ≡ a (mod m). What is the probability that this property fails for any integers 'a' and 'b' that already satisfy the premise?
�� Symmetry is always true. �� Congruence is an equivalence relation. �� Failure never occurs.
If a ≡ b (mod m), then m divides (a − b). Consequently, m also divides −(a − b) = (b − a). Therefore b ≡ a (mod m). Since symmetry always holds, the probability of failure is zero. Other options incorrectly assume possible exceptions.
- �� Option A → Failure never occurs.
- �� Option B → No probabilistic uncertainty exists.
- �� Option D → Symmetry does not depend on modulus choice.
Used: Elimination
Application: Use the definition of congruence and sign reversal.
Final Logic: Divisibility of a−b automatically implies divisibility of b−a.
"Reverse sign, same divisibility."
10 In establishing the reflexive property, vectorially calculating m | (a - a) yields 0. What does this mean for the relation a ≡ a (mod m)?
�� a − a = 0. �� Every integer m divides 0. �� Reflexive property always holds.
Since a − a = 0 and every nonzero integer divides 0, the condition m | (a − a) is always satisfied. Therefore a ≡ a (mod m) for every integer a. This establishes reflexivity. Options B, C, and D unnecessarily restrict or deny the property.
- �� Option B → Reflexivity applies to all integers.
- �� Option C → The relation is valid.
- �� Option D → Reflexivity is true for every modulus m.
Used: Substitution
Application: Replace a−a with zero and apply divisibility.
Final Logic: m divides 0, so a ≡ a (mod m).
"Self minus self = 0."
11 Suppose a ≡ b (mod m) and b ≡ c (mod m). By substituting b = a + km and c = b + k'm, the calculated area of difference (c - a) is equal to:
�� Use the given substitutions. �� Replace b in c = b + k'm. �� Difference becomes a multiple of m.
Given b = a + km and c = b + k'm. Substituting b into c gives c = a + km + k'm = a + (k + k')m. Therefore c − a = (k + k')m. This proves divisibility by m and establishes transitivity. Other options omit or incorrectly combine the coefficients.
- �� Option A → Uses subtraction instead of addition of coefficients.
- �� Option C → Ignores the contribution of k'm.
- �� Option D → Ignores the contribution of km.
Used: Substitution
Application: Substitute the first congruence expression into the second and simplify.
Final Logic: c − a = (k + k')m, hence divisible by m.
"Transitive ⇒ add the multiples."
12 The relation Rm defined by a Rm b if and only if a ≡ b (mod m) is an equivalence relation because it integrates which specific properties?
�� Equivalence relations have three defining properties. �� Reflexive, symmetric, and transitive are mandatory. �� Congruence satisfies all three.
A relation is an equivalence relation only when it is reflexive, symmetric, and transitive. Congruence modulo m satisfies all these properties: a ≡ a, a ≡ b implies b ≡ a, and a ≡ b with b ≡ c implies a ≡ c. The remaining options describe algebraic operations rather than equivalence criteria.
- �� Option A → These are arithmetic operations, not equivalence properties.
- �� Option C → These are algebraic laws of operations.
- �� Option D → These are related concepts but not defining properties.
Used: Odd One Out
Application: Identify the standard three-property definition of equivalence relations.
Final Logic: Only reflexive, symmetric, and transitive characterize equivalence relations.
"RST = Relation Stays True."
13 Which statement accurately represents the fact that equivalence classes [0], [1], ..., [m−1] for mod m are "non-overlapping sets"?
�� Distinct classes are disjoint. �� No element belongs to two different classes. �� Their intersections are empty.
Equivalence classes partition a set. In modulo arithmetic, every integer belongs to exactly one residue class. Therefore any two different classes have no common element and their intersection is empty. Option A contradicts disjointness. Option C is false. Option D is incorrect because their union forms the entire set of integers.
- �� Option A → Distinct classes cannot share elements.
- �� Option C → Not every class contains m.
- �� Option D → Union of all classes covers all integers.
Used: Elimination
Application: Recall the partition property of equivalence classes.
Final Logic: Different equivalence classes are mutually disjoint.
"One number, one class."
14 The total number of exact equivalence classes for modulo m is represented as [0], [1], ..., up to what final class?
�� Possible remainders are 0 to m−1. �� Each remainder forms one class. �� Final class is [m−1].
Modulo m arithmetic allows only remainders 0, 1, 2, ..., m−1. Each remainder corresponds to one equivalence class. Hence there are exactly m classes, ending with [m−1]. Options A and B introduce invalid remainder values, while D ignores the finite nature of residue classes.
- �� Option A → Remainder m is equivalent to remainder 0.
- �� Option B → Impossible remainder in modulo m.
- �� Option D → Number of classes is finite.
Used: Elimination
Application: List all permissible remainders modulo m.
Final Logic: Residue classes correspond exactly to remainders 0 through m−1.
"Modulo m ends at m−1."
15 Find all the positive integers strictly less than 30 forming the equivalence class of 5 for modulo 7.
�� Numbers must be congruent to 5 mod 7. �� Add successive multiples of 7. �� Keep values below 30.
The class [5] modulo 7 consists of numbers of the form 5 + 7k. Taking positive values less than 30 gives 5, 12, 19, and 26. Option B contains multiples of 7. Option C does not maintain remainder 5. Option D includes 33, which exceeds the limit.
- �� Option B → These belong to class [0].
- �� Option C → Several numbers have different remainders modulo 7.
- �� Option D → 33 is not less than 30.
Used: Substitution
Application: Generate values using 5 + 7k and apply the upper bound.
Final Logic: Only Option A contains all valid members below 30.
"Class [5] = 5 + 7k."
16 Find the positive integers less than 50 forming the equivalence class 4 for modulo 6.
�� Numbers must leave remainder 4. �� Pattern is 4 + 6k. �� All values remain below 50.
The equivalence class [4] modulo 6 contains all integers of the form 4 + 6k. Listing positive values less than 50 yields 4, 10, 16, 22, 28, 34, 40, and 46. Other options contain numbers belonging to different remainder classes.
- �� Option B → Multiples of 6 belong to class [0].
- �� Option C → Contains numbers with varying remainders.
- �� Option D → Not all values leave remainder 4 modulo 6.
Used: Substitution
Application: Use the formula 4 + 6k and generate valid terms.
Final Logic: Only Option A contains all numbers congruent to 4 modulo 6.
"Class [4] = 4 + 6k."
17 What distinguishes a Simple Arithmetic Function from a general algebraic function?
�� Arithmetic functions are number-theoretic functions. �� Inputs are positive integers. �� Outputs may be real or complex.
A simple arithmetic function is defined primarily on positive integers and studies arithmetic properties of numbers. Its range may be real or complex. Option B imposes an incorrect domain. Option C wrongly restricts outputs. Option D contradicts the very definition of a mathematical function.
- �� Option B → Negative fractions are not the defining domain.
- �� Option C → Outputs need not be imaginary.
- �� Option D → Functions always obey a defining rule.
Used: Elimination
Application: Identify the defining characteristic from the definition.
Final Logic: Arithmetic functions are distinguished by a positive-integer domain.
"Arithmetic ⇒ Acts on integers."
18 For the arithmetic function mapping Z+ → R, if f(x) = x², what is the image if the pre-image is 5?
�� Substitute x = 5. �� Compute 5². �� Result equals 25.
The function rule is f(x) = x². Replacing x with 5 gives f(5) = 5² = 25. Therefore the image corresponding to the pre-image 5 is 25. The remaining options do not satisfy the function rule and arise from incorrect computation.
- �� Option A → Returns the input unchanged.
- �� Option B → Represents multiplication by 2, not squaring.
- �� Option D → Not produced by f(5).
Used: Substitution
Application: Insert the given input into the function formula.
Final Logic: 5² = 25, so Option C is correct.
"Square 5 → 25."
19
If an arithmetic function machine is set to the rule f(x) = 3x + 1, and the pre-image is 4 (a positive integer), what is the generated image?
�� Use the function rule. �� Substitute x = 4. �� Evaluate 3(4) + 1.
The machine follows the rule f(x) = 3x + 1. For pre-image 4, f(4) = 3 × 4 + 1 = 13. Therefore the generated image is 13. Option A omits the added 1, while Options C and D do not satisfy the stated function rule.
- �� Option A → Uses only 3 × 4.
- �� Option C → Confuses input with output.
- �� Option D → Does not follow the function definition.
Used: Substitution
Application: Insert the input value into the machine rule.
Final Logic: f(4) = 12 + 1 = 13.
"Triple then add one."
20
Why are Simple Arithmetic functions widely useful according to the passage?
�� Directly stated in the passage. �� Arithmetic functions study number properties. �� Important in number theory.
The passage explicitly states that simple arithmetic functions describe arithmetic properties of numbers and are widely useful in number theory. Therefore Option B is correct. Options A, C, and D introduce ideas not mentioned in the passage and are unrelated to the stated purpose of arithmetic functions.
- �� Option A → Geometry graphs are not discussed.
- �� Option C → Negative roots are unrelated to the passage.
- �� Option D → This is not the defining purpose of arithmetic functions.
Used: Contextual/Tonal Matching
Application: Locate the exact statement in the passage and match it with the options.
Final Logic: Option B directly reproduces the passage's key idea.
"Arithmetic function = Number property tool."
