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

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Math Expert
Joined: 02 Sep 2009
Posts: 51035
The average (arithmetic mean) of four numbers is 4a + 16. When a fifth  [#permalink]

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23 Aug 2018, 23:40
00:00

Difficulty:

15% (low)

Question Stats:

84% (00:59) correct 16% (00:56) wrong based on 38 sessions

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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

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

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23 Aug 2018, 23:45
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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24 Aug 2018, 01:12
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.

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

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24 Aug 2018, 07:16
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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Abhishek....

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Re: The average (arithmetic mean) of four numbers is 4a + 16. When a fifth &nbs [#permalink] 24 Aug 2018, 07:16
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