Question

the ratio of red marbles to blue marbles in a bag is 4:7. there ARE 16 RED MARBLES HOW MANY BLUE MARBLES ARE THERE

Answer 1

what you got here is a proportion

first let me explain that the ratio 4:7 can also be written as 4/7.

4/7 = 16/x ---(4 red to 7 blue = 16 red to x blue)
as with any proportion, we now cross multiply
(4)(x) = (16)(7)
4x = 112 -- now divide both sides by 4
x = 28

we can even check to see if our answer is correct..
4/7 = 16/28 -- cross multiply
(4)(28) = (7)(16)
112 = 112 (correct)

so if he has 16 red marbles, then he has 28 blue ones

any questions ?