Probability
posted by Meg .
a bag contains 9 red marbles and 4 blue marbles. how many clear marbles should be added to the bag so the probibility of drawing a red marble is 3/5?????

let the number of clear marbles added be x
so prob of drawing a red
= 9/(13+x)
9/(13+x) = 3/5
39 + 3x =45
3x= 6
x = 2
2 clears should be added
check:
now the number of marbles would be 15
(9 red, 4 blue, 2 clear)
prob of a red = 9/15 = 3/5