The ratio of red jelly beans to yellow ones is 3:4. If I eat 3 red ones and 6 yellow ones, the ratio is 4:5. How many yellow ones to begin with?

Answer 1

number of reds ---- 3x
number of yellows -- 4x

(3x-3)/(4x-6) = 4/5
16x - 24 = 15x - 15
x = 9

number of reds at the start = 3(9) = 27
number of yellows at the start = 4(9) = 36

check: origianl ratio = 27/36 = 3/4
after "eating" ratio = 24/30 = 4/5