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# The average of seven numbers is 3. Out of these numbers, the average

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Math Expert
Joined: 02 Sep 2009
Posts: 53020
The average of seven numbers is 3. Out of these numbers, the average  [#permalink]

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28 Jan 2019, 03:15
1
00:00

Difficulty:

25% (medium)

Question Stats:

81% (01:31) correct 19% (03:09) wrong based on 20 sessions

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The average of seven numbers is 3. Out of these numbers, the average of first four numbers is 4 and the average of last four numbers is 4. Then, what is the fourth number?

A. 10

B. 11

C. 12

D. 13

E. 15

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Joined: 09 Mar 2018
Posts: 1001
Location: India
The average of seven numbers is 3. Out of these numbers, the average  [#permalink]

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Updated on: 29 Jan 2019, 07:05
Bunuel wrote:
The average of seven numbers is 3. Out of these numbers, the average of first four numbers is 4 and the average of last four numbers is 4. Then, what is the fourth number?

A. 10

B. 11

C. 12

D. 13

E. 15

IMO B

Let a b c d e f & g be the 7 numbers

a+b+c+d+e+f+g = 21
[a+b+c+e+f+g]= 21 - d

a+b+c+d = 16 & d+e+f+g = 16

a+b+c+2d+e+f+g = 32

2d = 32 - [a+b+c+e+f+g]

2d = 32 - 21 +d
d = 11

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Quote which i can relate to.
Many of life's failures happen with people who do not realize how close they were to success when they gave up.

Originally posted by KanishkM on 28 Jan 2019, 03:29.
Last edited by KanishkM on 29 Jan 2019, 07:05, edited 1 time in total.
VP
Joined: 31 Oct 2013
Posts: 1138
Concentration: Accounting, Finance
GPA: 3.68
WE: Analyst (Accounting)
Re: The average of seven numbers is 3. Out of these numbers, the average  [#permalink]

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28 Jan 2019, 03:37
Bunuel wrote:
The average of seven numbers is 3. Out of these numbers, the average of first four numbers is 4 and the average of last four numbers is 4. Then, what is the fourth number?

A. 10

B. 11

C. 12

D. 13

E. 15

Sum of 7 numbers = 7*3 = 21

Sum of first 4 = 4*4 = 16

Sum of last 4 = 4*4 = 16.

NOTE: 4th number has been added 2 times. Therefore :

16 + 16 - 21

32 - 21 = 11.

.
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Joined: 18 Aug 2017
Posts: 1883
Location: India
Concentration: Sustainability, Marketing
GPA: 4
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Re: The average of seven numbers is 3. Out of these numbers, the average  [#permalink]

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28 Jan 2019, 05:22
Bunuel wrote:
The average of seven numbers is 3. Out of these numbers, the average of first four numbers is 4 and the average of last four numbers is 4. Then, what is the fourth number?

A. 10

B. 11

C. 12

D. 13

E. 15

sum of 1st four = 16
last four = 16
and total = 21
so middle no 16+16-21 = 11
IMO B
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Re: The average of seven numbers is 3. Out of these numbers, the average   [#permalink] 28 Jan 2019, 05:22
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