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Which of the following pair of numbers is relatively prime to each other?

Solution

✅ Correct Option: 3

Two numbers are relatively prime (coprime) when they have no common factors except 1. This means their Greatest Common Divisor (GCD) = 1.

For each pair, find the GCD. If GCD = 1, the numbers are relatively prime. If GCD > 1, they are not relatively prime.


Option 1: (371, 159)

Using the Euclidean Algorithm:

371 ÷ 159 = 2 remainder 53

159 ÷ 53 = 3 remainder 0

GCD = 53 (NOT relatively prime)


Option 2: (407, 259)

407 ÷ 259 = 1 remainder 148

259 ÷ 148 = 1 remainder 111

148 ÷ 111 = 1 remainder 37

111 ÷ 37 = 3 remainder 0

GCD = 37 (NOT relatively prime)


Option 3: (95, 112)

95 is odd (ends in 5) and 112 is even (ends in 2), so they don't share the factor 2.

95 = 5 × 19

112 = 242^4 × 7

No common factors exist.

GCD = 1 (RELATIVELY PRIME)


Option 4: (57, 123)

Both are divisible by 3:

Sum of digits of 57: 5 + 7 = 12 (divisible by 3)

Sum of digits of 123: 1 + 2 + 3 = 6 (divisible by 3)

GCD = 3 (NOT relatively prime)


The answer is Option 3: (95, 112)

These numbers share no common factors except 1, making them relatively prime.

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