A jar contains 20 marbles: 4 red, 6 white, and 10 blue. If you remove marbles one at a time, randomly, what is the minimum number that must be removed to be certain that you have at least 2 marbles of each colour ?
In a certain college the number of girls is twice the number of boys. 1/5th of the girls and 1/8th of the boys took part in a social camp. What part of the total number of students took part in the camp ?