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=2×2×3 15=3×5 20=2×2×5 LCM =2×2×3×5 ⇒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