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Find the smallest number which when increased by 20 is completely divisible by 12, 20, 15, 18 and 24.
Question

Find the smallest number which when increased by 20 is completely divisible by 12, 20, 15, 18 and 24.

A.

320

B.

330

C.

340

D.

310

Correct option is C

Given:
Divisors = 12, 15, 18, 20, 24
The number is increased by 20 to be perfectly divisible.
Formula Used:
Required number = LCM(a, b, c, ...) - Increment
Solution:
Find the Lowest Common Multiple (LCM) of 12, 15, 18, 20, and 24.
Prime factorization:
12 = 22×32^2 \times 3​​
15 = 3×5 3 \times 5​​
18 =  2×322 \times 3^2​​
20 = 22×52^2 \times 5​​
24 = 23×3 2^3 \times 3​​
LCM = 23×32×5=8×9×52^3 \times 3^2 \times 5 = 8 \times 9 \times 5​ = 360
The smallest number completely divisible by all given divisors is 360.
Since the number is increased by 20 to get 360, subtract 20 from the LCM:
360 - 20 = 340
Final Answer
So the correct answer is (c)

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