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Question

Two positive integers have HCF = 12 and LCM = 924. If one of the numbers is 84, what is the other number?

This question was previously asked in
RRB ALP 2025 CBT 2 Wiremen Question Paper (28-Jul-2026) (Shift 2)
The correct answer is
132

Finding the Other Number Using HCF and LCM

We are given the Highest Common Factor (HCF), the Least Common Multiple (LCM), and one of the two positive integers. We need to find the second integer.

Key Formula: For any two positive integers, let's say \(a\) and \(b\), the product of the integers is equal to the product of their HCF and LCM.

\( a \times b = HCF(a, b) \times LCM(a, b) \)

Applying the Formula

Let the two positive integers be \(a\) and \(b\). We are given:

  • HCF = 12
  • LCM = 924
  • One number, let's say \(a = 84\)
  • We need to find the other number, \(b\).

Calculation Steps

Substitute the known values into the formula:

\( 84 \times b = 12 \times 924 \)

Now, solve for \(b\):

\( b = \frac{12 \times 924}{84} \)

First, calculate the product of HCF and LCM:

\( 12 \times 924 = 11088 \)

Now, divide this product by the known number (84):

\( b = \frac{11088}{84} \)

Performing the division:

\( b = 132 \)

Therefore, the other number is 132.

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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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