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Maths MCQ - LCM and HCF

11 Three numbers are in the ratio of 3 : 4 : 5 and their LCM is 2400. Their HCF is

Let the numbers be 3x, 4x and 5x.
Then, their LCM =60x
So, 60x = 2400 => x = 40
⇒ The numbers are (3 × 40), (4 × 40) and(5 × 40).
Hence, required HCF = 40

12 What is the LCM of 1/3, 2/9, 5/6 and 4/27 ?

13 Two numbers are in ratio of 3 : 4 and LCM is 84. Which is the larger number of these two numbers?

Let the numbers be 3x and 4x
and LCM of (3x and 4x) = 84
=> 12x = 84
=> x = 7
So, numbers are 21 and 28.
Larger number =28.

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Question:

The total number of prime factors which are contained in (30)6 is

A. 15.
B. 16.
C. 17.
D. 18.

Correct answer: D

Explanation:

(30)6 = 26 X 36 X 56. :. Number of prime factors - 6 + 6+ 6 = 18.

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