The average (arithmetic mean) of four numbers is 5.5. When an additional number is included, the average of all five num

The average (arithmetic mean) of four numbers is 5.5. When an additional number is included, the average of all five numbers is 6. What is the additional number?

A. 5.75
B. 6.5
C. 8.0
D. 22.0
E. 30.0

Answer: C

Source: Princeton Review

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kapil99: Newbie | Next Rank: 10 Posts; Posts: 2; Joined: Thu Nov 19, 2020 8:15 am

Re: The average (arithmetic mean) of four numbers is 5.5. When an additional number is included, the average of all five

by kapil99 » Thu Nov 19, 2020 8:21 am

Sum of 4 numbers= 5.5X4= 22
Let the additional number be x
(22+x)/5 = 6
Therefore, x= 30-22= 8

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Scott@TargetTestPrep: GMAT Instructor; Posts: 7247; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

Re: The average (arithmetic mean) of four numbers is 5.5. When an additional number is included, the average of all five

by Scott@TargetTestPrep » Mon Nov 30, 2020 10:52 am

M7MBA wrote: ↑
Thu Nov 19, 2020 8:17 am
The average (arithmetic mean) of four numbers is 5.5. When an additional number is included, the average of all five numbers is 6. What is the additional number?

A. 5.75
B. 6.5
C. 8.0
D. 22.0
E. 30.0

Answer: C

Solution:

The sum of the original four numbers is 5.5 x 4 = 22, and the sum of the four numbers and the additional number is 6 x 5 = 30. Therefore, the additional number must be 30 - 22 = 8.

Answer: C

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