Question

A bag contains 5 red marbles and 4 green marbles.

What is the probability of choosing a red marble then a green marble, without replacement?

A.) 25/81
B.) 5/18
C.) 25/72
D.) 20/81

Answer 1

Correct choice is B

Explanation:

A bag contains 5 red marbles and 4 green marbles, 9 marbles in total.

The probability of choosing a red marble is

`Pr(\text{1st marble is red})=(5)/(9).`

After choosing the red marble, 8 marbles left. Then the probability of choosing a green marble is

`Pr(\text{2nd marble is green})=(4)/(8)=(1)/(2).`

Hence, the probability of choosing a red marble then a green marble, without replacement is

`Pr=(5)/(9)\cdot (1)/(2)=(5)/(18).`