Question

The ratio of blue marbles to yellow marbles in a jar is 7 to 9. If there are 28 blue marbles in the jar, how many yellow marbles are there?

Answer 1

Blue:Yellow = 7:9
Set up a proportion:
7/9 = 28/x ---->> cross multiply
252 = 7x ------>> divide by 7 on each side
x = 36 yellow marbles
To check:
You multiply 7 by 4 to get 28, so in order for the answer to be true, the same has to be done to the bottom, too.
9 times 4 = 36 (correct)

Answer 2

b : y = 7 : 9
b = 28
28 : y = 7 : 9
7 y = 28 * 9
7 y = 252
y = 252 : 7
y = 36
There are 36 yellow marbles.