A bag contains 3 red, 4 white and 5 blue balls. Arif begins removing balls from the bag at random, one at time, What is the least number of balls he must remove to be sure that he has at least one of each colour?

Here, Number of red ball =3  white ball=4 blue ball=5 suppose, one picked five balls there is a possiblity that all of them are blue balls. then again,if one picked another 4 balls (total 9) then there is a possiblity that all of them are Blue and White.

After that if one picked only one ball, then 10th ball must will be red. so,total balls he must pick=5+4+1 =10