Nihit wrote:

A drawer holds 4 red hats and 4 blue hats. What is the probability of getting exactly three red hats or exactly three blue hats when taking out 4 hats randomly out of the drawer and returning each hat before taking out the next one?

a) 1/8

b) ¼

c) ½

d) 3/8

e) 7/12

first draw:

first hat could be anyhthing so prob = 1

second hat could be anyhthing so prob is again = 1

third hat could be the same as either the first one or the second one. so prob = 1/2

fourth hat has to be the same as the third one. so prob = 1/2

so it is: (1/1 x 1/1 x 1/2 x 1/2) = 1/4

second draw:

first hat could be anyhthing so prob = 1

second hat must be the color that was only one in first draw. so prob = 1/2

third hat has to be the same as the second one above. so prob = 1/2

fourth hat has to be the same as second/third ones. so prob = 1/2

so total prob = 1/4 + 1/8 = 3/8

_________________

Verbal: http://gmatclub.com/forum/new-to-the-verbal-forum-please-read-this-first-77546.html

Math: http://gmatclub.com/forum/new-to-the-math-forum-please-read-this-first-77764.html

Gmat: http://gmatclub.com/forum/everything-you-need-to-prepare-for-the-gmat-revised-77983.html

GT