There are 10 marbles in a bag, and the marbles are either red or blue. Eric will randomly choose two marbles from the bag, without replacing the first one. How many BLUE marbles are in the bag given that the probability of both marbles will be red is 2 15?

Question

Vicente Mcfarland

Geography

17 May, 11:15

There are 10 marbles in a bag, and the marbles are either red or blue. Eric will randomly choose two marbles from the bag, without replacing the first one. How many BLUE marbles are in the bag given that the probability of both marbles will be red is 2 15?

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Answers (1)

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Yazmin Hensley · Answer 1

6 blue marbles

Explanation:

(red / 10) * (red minus one / 9)

r (r-1) / 90

2/15 = 12/90

r (r-1) / 90 = 12/90

r² - r = 12

r² - r - 12 = 0

(r + 3) (r - 4) = 0

r = - 3 or r = 4

red = 4; blue = 6