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Bunuel
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

\(Avg = \frac{Sum}{# of terms}\) so 5.5 = \(\frac{sum}{4}\)

Sum = 5.5 * 4 = 4 *5 + 4* 1/2 = 20 + 2 = 22

\(\frac{(22+x)}{5} = 6\)

30 = 22 + x

x = 8
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Bunuel
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


Sum of 4 numbers = 4*5.5 = 22

Sum of 5 numbers = 5*6 = 30

Difference = 30 -22 = 8.

The best answer is C.
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Bunuel
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
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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