What will be the least number which when doubled will be exactly divisible by 24, 18, 21 and 15?

1260

The correct answer is Option (3) → 1260

We need the least number ( x ) such that 2x is divisible by 24, 18, 21, and 15.

Step 1: Find LCM of 24, 18, 21, 15

24 = (2³ × 3)  
18 = (2 × 3²)  
21 = (3 × 7)  
15 = (3 × 5)  

LCM = (2³ × 3² × 5 × 7 = 8 × 9 × 5 × 7 = 2520)

Step 2: Since 2x = 2520  
⇒ x = 2520 ÷ 2 = 1260  

Hence, the least number is 1260.