Question:

Ten boxes each hold one white ball and one coloured ball every colour being different. Find the number of ways in which one ball may be taken from each box if half those taken are white.

10 boxes 10 choices 2 balls in each box but half of them already taken to be white

so there are 5 boxes left with 2 choices 5C2

so; 5 x 5C2 = 50

but the answer in the textbook is 252

Please help I am having difficult in understanding the question