Question

A box contains 4 marbles one of the marbles are red the rest are yellow. the probability that anatonia and sergio take a yellow marble is 0.7 how many marbles were originally in the box

Answer 1

Step-by-step explanation:

Let A = Event that the First Marble is Yellow.

Let B = Event that the 2nd Marble is Yellow.

Let P(B|A) = probability that event B happens assuming that event A has happened.

0.7 = P(A) P(B|A)

P(A) = (N - 4) / N

P(B|A) = (N - 5) / (N-1)

We need to solve:

0.7 = ((N-4) / N) ( (N-5) / (N-1))

0.7 (N) (N-1) = (N-4) * (N-5)

(0.7) (N2 - N ) = N2 - 9N + 20

0.7N2 - 0.7N = N2 - 9N + 20

0 = 0.3N2 - 8.3N + 20

0 = 3N2 - 83N + 200

N = 2.667 or 25

Allowed values for N are positive integers great than 5.

N = 25, answer.