Question

Suppose you know there are originally 2 red marbles in the bag. How many marbles are there in all? Show your work.

Answer 1

not enough info

Answer 2

The probability of randomly selecting a red marble from a bag, replacing it, and selecting a red marble again is 1/25

Answer 3

The probability of getting a red marble is 2/x where x is the total number of marbles.
Then the probability of randomly selecting a red marble, replacing it, and selecting a red marble again is (2/x)(2/x).

Therefore, (2/x)(2/x)=1/25
4/x^2=1/25
4=(1/25)(x^2)
(4)(25)=x^2
100=x^2
10=x

Therefore, there are 10 marbles in all