Madhya Pradesh Police Exam Model Paper 3

Concept used:
LCM will be the smallest number divisible by all of the numbers and the required answer will be the multiple of LCM
Calculation:
$12=2\times 2\times 3$
$15=3\times 5$
$20=2\times 2\times 5$
LCM $=2\times 2\times 3\times 5$
$\Rightarrow 60$
Out of the 4 options, 900 is the multiple of 60 and also a perfect square
∴ The smallest number which is divisible by 12, 15 and 20 and also is a perfect square is 900