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swerve: Legendary Member; Posts: 2499; Joined: Sun Oct 29, 2017 2:04 pm; Followed by:6 members

The average age of a group of 5 members is 20 years...

by swerve » Wed Jan 03, 2018 7:16 am

The average age of a group of 5 members is 20 years. Two years later, a new member joins the group. The average age of the group becomes 22 years. What is the age of the new member?

A. 20 years
B. 21 years
C. 22 years
D. 23 years
E. 24 years

The OA is C.

Please, can any expert explain this PS question for me? I tried to solve it but i'm not sure because the answer is so obvious! I need your help. Thanks.

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Source: Beat The GMAT — Problem Solving | Wed Jan 03, 2018 7:16 am

GMAT/MBA Expert

[email protected]: 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] » Wed Jan 03, 2018 10:53 am

Hi swerve,

We're told that the average age of a group of 5 members is 20 years. TWO years LATER, a new member joins the group and the average age of the group becomes 22 years. We're asked for the age of the new member.

This question doesn't require any heavy calculations IF you recognize the 'twist' involved. With the original group of 5 members who have an average age of 20, when you move that group 2 years into the future, the average age would be 22 (since they would all be 2 years older). So, by including a 6th person to that group and having the average STAY 22, the age of the 6th person must be 22.

Final Answer: C

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

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Scott@TargetTestPrep: 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 » Mon Sep 02, 2019 6:09 pm

swerve wrote:The average age of a group of 5 members is 20 years. Two years later, a new member joins the group. The average age of the group becomes 22 years. What is the age of the new member?

A. 20 years
B. 21 years
C. 22 years
D. 23 years
E. 24 years

The OA is C.

Please, can any expert explain this PS question for me? I tried to solve it but i'm not sure because the answer is so obvious! I need your help. Thanks.

If the new member has not joined the group, the average age of the group is 22 years (since 2 years earlier their average age was 20). Therefore, in order for the new member to keep the average age of the group as 22, he or she is also 22 years old.

Answer: C

Scott Woodbury-Stewart
Founder and CEO
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