There are 5 red rocks 6 white rocks and 4 blue rocks in a sa

There are 5 red rocks, 6 white rocks, and 4 blue rocks in a sack.

Write all answers to the nearest 10th of a percent.

(1) What is the probability of selecting a rock that is red?

(2) What is the probability of selecting one red rock or one white rock?

(3) What is the probability of selecting a rock, putting it back, and selecting another that are both blue?

(4) What is the probability of selecting a rock, putting it down, and selecting another that are both white?

(5) What is the probability of selecting a rock that is red, putting it down, and selecting another that is white?

Solution

There are a total of 15 rocks here.

1)

P(red) = 5 red/15 rocks = 0.33333333 = 33.3% [answer]

*******

2)

P(red or white) = (5 red + 6 white)/15 = 0.733333333 = 73.3% [answer]

*********

3)

P(both blue) = P(blue) P(blue) = (4 blue/15)(4 blue/15) = 0.071111111 = 7.1% [answer]

***********

4)

P(both white) = P(white) P(white) = (6 white/15)(6 white/15) = 0.071111111 = 16% [answer]

**********

5)

P(red then white) = P(red) P(white) = (5 red/15)(6 white/15) = 0.133333333 = 13.3% [answer]