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

Question

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

Bunuel · Accepted Answer

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 average age of a group of 5 members is 20 years --> the sum of the ages is 5*20=100;
 Two years later  the sum of the ages of these 5 members would be 100+5*2=110;

Now, say the age of the new member is x years, so the sum of the ages of a new 6 member group is 110+x. Since given that the average age of this group of 6 members is 22 years then: 22*6=110+x --> x=22.

Answer: C.

GyanOne · Answer

The average age of the 5 members is 20 years
=> The sum of the ages of the 5 members is 20*5 = 100 years

Once the new member joins, the average age becomes 22 years. 
Let the age of the new member be x. 
Then (110+x)/6 = 22
=> x = 22 years

@Bunuel: Thx!

LalaB · Answer

IMHO, this question will be trickier, if answer choice (32) is added

kraizada84 · Answer

sum(age of 5 members=a)= 20*5
sum(a+b+10) = 22*6
b= 22*6- 20*5-10= 132 - 100-10 = 22

Hence C

Bunuel · Answer

Bumping for review and further discussion*. Get a kudos point for an alternative solution!

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vs129 · Answer

Two years later, avg age of group will be 22 , since 2 has been added to everyones' age. Since this average is unchanged when the new member is added, his age must also be 22.

PareshGmat · Answer

Answer to this lies in the question only

Current Average = 20 After 2 yrs, average would be = 22 Given that post joining of new member, average still remains 22 No effect of average, means the person who joins, his age = 22

PareshGmat · Answer

I would rather say, if the average after addition would had been changed from 22 to some other number,

then calculation might be required making this time consuming

stonecold · Answer

Mean 1=> 20
Mean 2=> 100+10/5=> 22
Mean 3=> 22
Here,as Mean 2=Mean 3=> The age of the new guy must be 22yrs.only.

Hence C

ScottTargetTestPrep · Answer

Before the new member joins 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 must also be 22 years old.

Answer: C

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

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