A bag contains 6 red marbles, 5 yellow marbles, and 7 green marbles. How many additional red marbles must ...

Question

be added to the 18 marbles already in the bag so that the probablity of randomly drawing a red marble is 3/5?

Answer 1

12 red marbles.

You would then have 18 red marbles in a bag of 30.

18/30 = 3/5

You can come up with an algebraic expression to solve:

(x + 6)/(x + 18) = 3/5
"(# of red marbles + x) divided by (# of total marbles + x) equals the ratio 3/5"

Cross multiply to get:

5x + 30 = 3x + 54
2x = 24
x = 12

Answer 2

9 red marbles