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# If the average (arithmetic mean) of a and – 5 is 10, then a =

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Math Expert
Joined: 02 Sep 2009
Posts: 58445
If the average (arithmetic mean) of a and – 5 is 10, then a =  [#permalink]

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14 Jan 2019, 04:15
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Difficulty:

15% (low)

Question Stats:

87% (00:21) correct 13% (00:16) wrong based on 29 sessions

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If the average (arithmetic mean) of a and – 5 is 10, then a =

A. 25
B. 15
C. 5
D. -10
E. -15

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Joined: 02 Mar 2016
Posts: 2
Location: India
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Re: If the average (arithmetic mean) of a and – 5 is 10, then a =  [#permalink]

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14 Jan 2019, 04:39
avg= (a+(-5))/2 .............eq(1)
avg= 10 (given) .............eq(2)
from eq (1) and eq(2)
=> (a+(-5))/2=10
=> (a+(-5))=20
=> a-5 =20
=> a =25
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Re: If the average (arithmetic mean) of a and – 5 is 10, then a =  [#permalink]

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14 Jan 2019, 04:47
Bunuel wrote:
If the average (arithmetic mean) of a and – 5 is 10, then a =

A. 25
B. 15
C. 5
D. -10
E. -15

a + ( -5) / 2 = 10

a - 5 = 20

a = 25.

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Re: If the average (arithmetic mean) of a and – 5 is 10, then a =  [#permalink]

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14 Jan 2019, 05:02
$$\frac{a - 5}{2}$$ = 10

a = 25

OPTION: A
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Re: If the average (arithmetic mean) of a and – 5 is 10, then a =  [#permalink]

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14 Jan 2019, 18:59
Bunuel wrote:
If the average (arithmetic mean) of a and – 5 is 10, then a =

A. 25
B. 15
C. 5
D. -10
E. -15

We use the formula for the average to create the equation:

(a + (-5))/2 = 10

a - 5 = 20

a = 25

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Re: If the average (arithmetic mean) of a and – 5 is 10, then a =   [#permalink] 14 Jan 2019, 18:59
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