Ratio of two numbers is 3 : 2. If the LCM of the numbers is 60, then the…

2023

Ratio of two numbers is 3 : 2. If the LCM of the numbers is 60, then the smaller number is?

  1. A.

    20

  2. B.

    30

  3. C.

    40

  4. D.

    50

Attempted by 3 students.

Show answer & explanation

Correct answer: A

Concept:

When two numbers are in the ratio a : b with a and b coprime (no common factor besides 1), they can be written as a×x and b×x. Because a and b share no common factor, the LCM of the two numbers is simply a × b × x — both ratio terms multiply directly with x to form the LCM.

Application:

  1. Let the two numbers be 3x and 2x, since their ratio is 3 : 2 and 3, 2 are coprime.

  2. The LCM of 3x and 2x is 3 × 2 × x = 6x.

  3. Given LCM = 60, so 6x = 60, which gives x = 10.

  4. Smaller number = 2x = 2 × 10 = 20.

Cross-check:

The two numbers are 3 × 10 = 30 and 2 × 10 = 20. Since 30 = 2 × 3 × 5 and 20 = 22 × 5, their LCM is 22 × 3 × 5 = 60, confirming the working.

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