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The average (arithmetic mean) of four numbers is 4a + 16. When a fifth

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The average (arithmetic mean) of four numbers is 4a + 16. When a fifth  [#permalink]

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New post 24 Aug 2018, 00:40
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A
B
C
D
E

Difficulty:

  15% (low)

Question Stats:

84% (01:21) correct 16% (01:25) wrong based on 42 sessions

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Re: The average (arithmetic mean) of four numbers is 4a + 16. When a fifth  [#permalink]

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New post 24 Aug 2018, 00:45
Bunuel wrote:
The average (arithmetic mean) of four numbers is 4a + 16. When a fifth number is added, the average becomes 5a + 20. The fifth number is

A. a - 4
B. a + 4
C. 4a + 4
D. 4a + 16
E. 9a + 36


Sum of four numbers=4*(4a+16)
Sum of five numbers(when a fifth number is added)=5*(5a+20)

So, the 5th number=5*(5a+20)-4*(4a+16)=9a+36

Ans. (E)
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Re: The average (arithmetic mean) of four numbers is 4a + 16. When a fifth  [#permalink]

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New post 24 Aug 2018, 02:12
Bunuel wrote:
The average (arithmetic mean) of four numbers is 4a + 16. When a fifth number is added, the average becomes 5a + 20. The fifth number is

A. a - 4
B. a + 4
C. 4a + 4
D. 4a + 16
E. 9a + 36



Average of the 4 numbers = 4a + 16

Total of 4 numbers = 4 ( 4a + 16) = 16a + 64

Average of the 5 numbers = 5a + 20

Total of 5 numbers = 5 ( 5a + 20) = 25a + 100

Question: The 5th number:

25a + 100 - 16a -64 = 9a + 36.

The best answer is E.
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Re: The average (arithmetic mean) of four numbers is 4a + 16. When a fifth  [#permalink]

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New post 24 Aug 2018, 08:16
Bunuel wrote:
The average (arithmetic mean) of four numbers is 4a + 16. When a fifth number is added, the average becomes 5a + 20. The fifth number is

A. a - 4
B. a + 4
C. 4a + 4
D. 4a + 16
E. 9a + 36

\(16a + 64 + k = 25a +100\)

Or, \(k = 9a + 36\) , Answer must be (E)
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Re: The average (arithmetic mean) of four numbers is 4a + 16. When a fifth   [#permalink] 24 Aug 2018, 08:16
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