If a certain coin is flipped, the probability that the coin will land heads is 1/2. If the coin is flipped 5 times, what

This topic has expert replies
Moderator
Posts: 6693
Joined: 07 Sep 2017
Followed by:21 members

Timer

00:00

Your Answer

A

B

C

D

E

Global Stats

If a certain coin is flipped, the probability that the coin will land heads is 1/2. If the coin is flipped 5 times, what is the probability that it will land heads up on the first 3 flips and not on the last 2 flips?

A. 3/5
B. 1/2
C. 1/5
D. 1/8
E. 1/32



OA E

Source: GMAT Prep

Master | Next Rank: 500 Posts
Posts: 409
Joined: 15 Oct 2009
Thanked: 27 times
The question is asking for the probability of a set of outcomes which occur in a specific order.

Since each toss is independent of the other and each face has a 1/2 chance of appearing the probability is [spoiler]1/32, E[/spoiler]

If the question had asked for probability of 3 heads and 2 tails occurring in 5 tosses, then would need to consider all orders that produce the result

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16118
Joined: 08 Dec 2008
Location: Vancouver, BC
Thanked: 5254 times
Followed by:1268 members
GMAT Score:770
BTGmoderatorDC wrote:
Sat Jun 18, 2022 10:58 pm
If a certain coin is flipped, the probability that the coin will land heads is 1/2. If the coin is flipped 5 times, what is the probability that it will land heads up on the first 3 flips and not on the last 2 flips?

A. 3/5
B. 1/2
C. 1/5
D. 1/8
E. 1/32



OA E

Source: GMAT Prep
We want P(heads on 1st AND heads on 2nd AND heads on 3rd AND tails on 4th AND tails on 5th)
= P(heads on 1st) x P(heads on 2nd) x P(heads on 3rd) x P(tails on 4th) x P(tails on 5th)
= 1/2 x 1/2 x 1/2 x 1/2 x 1/2
= 1/32

Answer: E
Brent Hanneson - Creator of GMATPrepNow.com
Image