A box has 10 marbles in it, 2 red and 8 white. Suppose we draw a marble from the box, replace it, and then draw another. Find the probability that

(a) Both marbles are red
(b) Just one of the two marbles is red

Question

A box has 10 marbles in it, 2 red and 8 white. Suppose we draw a marble from the box, replace it, and then draw another. Find the probability that

(a) Both marbles are red
(b) Just one of the two marbles is red

anonymous · Answer

a) (1/5)(1/5)=1/25
b)(1/5)(4/5)=4/25

zarkon · Answer

hmmm...not real happy with your answer to (b) ;)

anonymous · Answer

what do you think it should be?

zarkon · Answer

8/25

anonymous · Answer

how did you get that?

zarkon · Answer

one red that mean  either the first is red 2nd is white or the 2nd is red and 1st iw white

$$\frac{2}{10}\frac{8}{10}+\frac{8}{10}\frac{2}{10}=\frac{8}{25}$$

anonymous · Answer

makes sense n since i wasnt sure go with that

zarkon · Answer

if you find the prob both are white you get 64/100

1/25+8/25+64/100=1

Law of total probability is satisfied