BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

What is the probability of getting only 1 head in a single

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Problem Solving |
User avatar
GMAT Instructor
Posts: 555
Joined: Wed Oct 04, 2017 4:18 pm
Thanked: 180 times
Followed by:12 members

by EconomistGMATTutor » Sat Feb 03, 2018 7:47 am
M7MBA wrote:What is the probability of getting only 1 head in a single throw of three fair coins?

A) 1/2
B) 3/8
C) 1/4
D) 1/5
E) 5/8

The OA is the option B.

How can I determine the correct answer? Shouldn't it be (1/2)^3=1/8? I am confused.<i class="em em-confused"></i>
Hi M7MBA.

Let's take a look at your question.

First, we have _ _ _ (3) places, and each place has 2 possibilities (H or T). Hence, there are a total of 2*2*2=8 possibilities.

Now, we want to obtain ONLY one head, this implies that we have the next cases:

HTT
THT
TTH

Therefore, there are 3 cases.

Finally, the answer is cases favorable / total of cases = 3/8. This is why the correct answer is B.

I hope this answer may help you.

Feel free to ask me again if you have any doubt.

Regards.
GMAT Prep From The Economist
We offer 70+ point score improvement money back guarantee.
Our average student improves 98 points.

Image
Top

GMAT/MBA Expert

User avatar
Elite Legendary Member
Posts: 10392
Joined: Sun Jun 23, 2013 6:38 pm
Location: Palo Alto, CA
Thanked: 2867 times
Followed by:511 members
GMAT Score:800

by [email protected] » Sat Feb 03, 2018 10:58 am
Hi M7MBA,

Since we're tossing just 3 coins, there aren't that many possible outcomes. This question can be solved simply by listing out the possibilities and answering the exact question that is asked. With 3 coins, there are (2)(2)(2) = 8 possible outcomes. They are...

HHH
HHT
HTH
THH

TTT
TTH
THT
HTT

We're asked for the probability of getting exactly 1 HEAD from those 3 tosses. There are three ways (out of 8 total) to get exactly 2 heads (HTT, THT and TTH).

Final Answer: B

GMAT assassins aren't born, they're made,
Rich
Contact Rich at [email protected]
Image
Top
User avatar
GMAT Instructor
Posts: 1462
Joined: Thu Apr 09, 2015 9:34 am
Location: New York, NY
Thanked: 39 times
Followed by:22 members

by Jeff@TargetTestPrep » Fri Feb 09, 2018 10:17 am
M7MBA wrote:What is the probability of getting only 1 head in a single throw of three fair coins?

A) 1/2
B) 3/8
C) 1/4
D) 1/5
E) 5/8
We need to determine the probability of H-T-T = 1/2 x 1/2 x 1/2 = 1/8.

Since H-T-T can be arranged in 3!/2! = 3 ways, the total probability is 3/8.

Answer: B

Jeffrey Miller
Head of GMAT Instruction
[email protected]

Image

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews
Top
Post new topic Post Reply
• Page 1 of 1