What is the probability of getting three heads in a row and

This topic has expert replies
Source: — Problem Solving |

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 3008
Joined: Mon Aug 22, 2016 6:19 am
Location: Grand Central / New York
Thanked: 470 times
Followed by:34 members

by Jay@ManhattanReview » Tue Jul 23, 2019 10:25 pm
swerve wrote:What is the probability of getting three heads in a row and then a tail on four flips of a coin?

A. \(\frac{1}{16}\)

B. \(\frac{2}{16}\)

C. \(\frac{3}{16}\)

D. \(\frac{4}{16}\)

E. \(\frac{5}{16}\)

The OA is A

Source: Veritas Prep
For an unbiased coin, upon flipping a coin

probability of getting a head = 1/2; and
probability of getting a tail = 1/2

Probability of getting 3 heads in a row = 1/2 * 1/2 * 1/2 = 1/8; and
Probability of getting a tail in the 4th flip = 1/2

Thus, the probability of getting three heads in a row and then a tail on four flips of a coin = 1/8 * 1/2 = 1/16

The correct answer: A

Hope this helps!

-Jay
_________________
Manhattan Review GMAT Prep

Locations: GMAT Manhattan | GRE Prep Courses Chicago | ACT Prep Courses Seattle | Boston IELTS Tutoring | and many more...

Schedule your free consultation with an experienced GMAT Prep Advisor! Click here.

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 8086
Joined: Sat Apr 25, 2015 10:56 am
Location: Los Angeles, CA
Thanked: 43 times
Followed by:29 members

by Scott@TargetTestPrep » Wed Jul 31, 2019 4:26 pm
swerve wrote:What is the probability of getting three heads in a row and then a tail on four flips of a coin?

A. \(\frac{1}{16}\)

B. \(\frac{2}{16}\)

C. \(\frac{3}{16}\)

D. \(\frac{4}{16}\)

E. \(\frac{5}{16}\)

The OA is A

Source: Veritas Prep

We need to determine P(HHHT).

Notice that there are 2^4 = 16 total outcomes in four flips of a coin and HHHT is one of the outcomes; therefore P(HHHT) = 1/16.

Answer: A

Scott Woodbury-Stewart
Founder and CEO
[email protected]

Image

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews

ImageImage