Prime factorization:
15 = 3 × 5
24 = 23 × 3
36 = 22 × 32
LCM = product of greatest power of each prime factor involved in the numbers = 23 × 32 × 5 = 360
Now, the greatest four digit number is 9999.
On dividing 9999 by 360 we get 279 as remainder.
Thus, 9999 – 279 = 9720 is exactly divisible by 360.
Hence, the greatest number of four digits which is exactly divisible by 15, 24 and 36 is 9720.
