Question

There are 3 red marbles, 2 blue marbles, and 7 black marbles if you choose one marble, what is the probability that it will be a red marble?

Answer 1

Probability of both red =3(182)=3(18!2!16!)=3153

Explanation:

Let Ai be the event in which the i-th ball you grab is red. For the first ball you choose, you have 3 red marbles out of a total of 18. Therefore,

P(A1)=318.

For the second marble you grab, given that you already took a red one, that is, given A1, you have 2 red balls out of a total of 17, then

P(A2∣A1)=217.

Finally,

P(A1∩A2)=P(A1)P(A2∣A1)=318217=151.

Answer 2

3:12

Explanation:

3 + 2 + 7 = 12

3 = red marbles

12 = total marbles