Question

Assuming the balls to be identical except for difference in colours, the number of ways in which one or more balls can be selected from 10 white, 9 green and 7 black balls is

Answer 1

heya it's Aastha...

Total number of ways in which a selection can be done by taking some or all out of (p+q+r...) items where p are alike , q are alike , r alike and so on is {(1+p)(1+q)(1+r)......}-1
here we have p = 10 , q=9 , r=7
thus , total number of ways  = {(1 + 10)(1 + 9)(1 + 7)} -1 = (11 * 10 * 8) - 1 = 880 - 1 = 879..

Hope it help you