Find the least 5-digit number which is exactly divisible by 20, 25, 30.

Least five digit number = 10000

L.C.M. of 20,25,30 is 300.
But we want the least five digit number which is divisible by 20, 25, 30.
So, we will multiply the L.C.M. by a number that makes it the least five digit number divisible by 20, 25, 30.
300$\times$31 = 9300
300$\times$32 = 9600
300$\times$33 = 9900
300$\times$34 = 10200

So, the least five digit number divisible by 20, 25, 30 is 10200.