GMAT Quantitative Reasoning Practice Test 1

Question : 21 of 100

Marks: +1, -0

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 immediately returning every hat to the drawer before taking
out the next?

$1 / 8$
$1 / 4$
$1 / 2$
$3 / 8$
$7 / 12$

Validate

Solution:

Getting three red out of 4 that are taken out has 4 options

(4! {/} (3! × 1!))

, each option has a probability of

(1/2)4

since drawing a red or blue has a

50%

chance.

4 × 1/16 = 1/4

to get three red hats. The same goes for three blue hats so

1/4+1/4 = 1/2.

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