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# If the average (arithmetic mean) of b and c is 5, and the average of c

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Math Expert
Joined: 02 Sep 2009
Posts: 58445
If the average (arithmetic mean) of b and c is 5, and the average of c  [#permalink]

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22 Aug 2018, 03:15
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Difficulty:

15% (low)

Question Stats:

86% (00:46) correct 14% (01:06) wrong based on 50 sessions

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If the average (arithmetic mean) of b and c is 5, and the average of c and d is 10, then b - d =

A. Cannot be determined
B. -5
C. -10
D. -15
E. -20

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Location: India
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Re: If the average (arithmetic mean) of b and c is 5, and the average of c  [#permalink]

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22 Aug 2018, 03:20
1
(b+c)/2 = 5.
b+c = 10.....(1)
Also given that (c+d)/2 = 10
c+d = 20.....(2)

Subtract 1 from 2 gives b-d = 10-20 = -10.

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If the average (arithmetic mean) of b and c is 5, and the average of c  [#permalink]

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22 Aug 2018, 05:27
Bunuel wrote:
If the average (arithmetic mean) of b and c is 5, and the average of c and d is 10, then b - d =

A. Cannot be determined
B. -5
C. -10
D. -15
E. -20

$$\frac{b + c}{2} = 5$$

b + c = 10......................................equation 1

again,

$$\frac{c + d}{2} = 10$$

c + d = 20.......................................equation 2.

deduct 2 from 1 :

(b + c) - (c + d) = b +c - c - d = b -d

10 - 20 = b- d

b - d = -10.

Director
Joined: 20 Feb 2015
Posts: 762
Concentration: Strategy, General Management
Re: If the average (arithmetic mean) of b and c is 5, and the average of c  [#permalink]

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22 Aug 2018, 13:27
Bunuel wrote:
If the average (arithmetic mean) of b and c is 5, and the average of c and d is 10, then b - d =

A. Cannot be determined
B. -5
C. -10
D. -15
E. -20

b+c=10 ------1
c+d=20 ------2

subtracting 1 from 2
b-d= -10
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Re: If the average (arithmetic mean) of b and c is 5, and the average of c  [#permalink]

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26 Aug 2018, 18:22
Bunuel wrote:
If the average (arithmetic mean) of b and c is 5, and the average of c and d is 10, then b - d =

A. Cannot be determined
B. -5
C. -10
D. -15
E. -20

We can create the equations:

(b + c)/2 = 5

b + c = 10

and

(c + d)/2 = 10

c + d = 20

Subtracting the second equation from the first we have:

b - d = -10

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Re: If the average (arithmetic mean) of b and c is 5, and the average of c   [#permalink] 26 Aug 2018, 18:22
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