Question

The probability of randomly selecting a red marble from a bag, replacing it, and selecting a red marble again is 1/25
Suppose you know there are originally 2 red marbles in the bag. How many marbles are there in all? Show your work.

Answer 1

50..... since you have 2 marbles to begin with you will have a 2/50 chance of drawing a red one.. thus if you reduce it its 1/25?

Answer 2

you have 10 marbles in all.

Answer 3

snap... why is it 10? lol

Answer 4

that would be 1/5?

Answer 5

the probability of selecting a red marble, REPLACING it and selecting another red marble is 1/25.
so the probability of these two events combined is 1/25.
which means P(A)*P(B) = 1/25.
since you are replacing the red marble, P(A) and P(B) are the same.
so the probability of selecting a red marble once is 1/5.
since there are 2 red marbles, there must be 10 total marbles for the probability of selecting a red marble to be 1/5

Answer 6

oh smarty.

Answer 7

thank you soooo much