add up all the fractions
1/2 + 1/8 + 1/5
find a common denominator, which is 40
20/40 + 5/40 + 8/40 = 33/40
subtract 40/40 -33/40 to find the fraction of white balls
= 7/40
Set up a proportion
7/40 = x/80
40 times 2 is 80 so 7 times 2 is 7
the number of white balls is 14.
hope this helps :)