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Question

Let N be the greatest number that will divide 600, 631 and 724, leaving the same remainder. What is the value of N ?

This question was previously asked in
CDS 1 2026 Maths Question Paper (12-Apr-2026)
The correct answer is

31

Greatest Number Problem Explained

The question asks for the greatest number, denoted as N, that divides 600, 631, and 724, ensuring the remainder is identical for each division.

Number N Differences Method

A key principle states that if a number N divides multiple numbers (say A, B, C) leaving the same remainder, then N must perfectly divide the differences between these numbers (A-B, B-C, A-C). We first calculate these differences:

  • Difference between 631 and 600: \(631 - 600 = 31\)
  • Difference between 724 and 631: \(724 - 631 = 93\)
  • Difference between 724 and 600: \(724 - 600 = 124\)

HCF Calculation for N

The greatest number N we are looking for is the Highest Common Factor (HCF) of these calculated differences: \(31\), \(93\), and \(124\).

To find the HCF, we list the prime factors for each difference:

  • Factors of \(31\): \(31\) (as it's a prime number)
  • Factors of \(93\): \(3 \times 31\)
  • Factors of \(124\): \(2 \times 2 \times 31\), which simplifies to \(4 \times 31\)

By comparing the factors, we see that \(31\) is the only common factor present in all three numbers. Therefore, the HCF(\(31\), \(93\), \(124\)) is \(31\).

Value of N Determined

The HCF represents the greatest number N that satisfies the condition.

Thus, the value of N is \(31\).

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Important Questions from LCM and HCF

  1. The greatest three-digit number which is divisible by 14, 28, and 42 is:

  2. What is the greatest number that will divide 209 and 347 leaving remainder 5 and 7 respectively?

  3. A number is three times another number and their HCF is 8. What is the sum of the squares of the numbers?

  4. The HCF of 2091, 3485 and 4879 is x. The sum of the digits of x is:

  5. If three numbers are in ratio of 3 : 5 : 7 and their LCM is 2415, what is the difference between the second number and the first number?

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