Question

There are 3 black marbles and 4 red marbles in a bag.

What is the probability of picking a black marble, replacing it back in the bag, and then choosing another black marble?

1) 3/8

2) 9/49

3) 5/13

4) 1/7

Answer 1

3 + 4 = 7 all marables in bag
The probability that the first marable is black

`P(A_1)=(3)/(7)`
The probability that the second marable is black

`P(A_2)=(3)/(7)`
Together:

`P(A)=P(A_1)\cdot P(A_2)=(3)/(7)\cdot(3)/(7)=(9)/(49)\to 2)`