math
posted by justin .
The number of Roberto's baseball cards is 3/4 the number of David's cards. If Roberto gives 1/2 of his cards to David, what will be the ratio of Roberto's cards to David's cards?

r = 3d/4, or 4r = 3d
r/2 / (3d/4 + r/2) = 2r/(3d+2r) = 2r/6r = 1/3
check:
If Roberto has 12 cards, David has 16
After Robert gives David 6,
6/18 = 1/3 
the number of roberto's baseball cards is 3/4 the number of david's cards. if roberto gives 1/2 of his cards to david, what will be the ratio of roberto's cards to david's cards?