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# If the average (arithmetic mean) of a and b is 65 and the average (ari

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Math Expert
Joined: 02 Sep 2009
Posts: 43349
If the average (arithmetic mean) of a and b is 65 and the average (ari [#permalink]

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25 Dec 2017, 00:31
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80% (00:31) correct 20% (00:51) wrong based on 15 sessions

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If the average (arithmetic mean) of a and b is 65 and the average (arithmetic mean) of b and c is 80, what is the value of c - a?

A. 90
B. 60
C. 30
D. 20
E. It cannot be determined from the information given.
[Reveal] Spoiler: OA

_________________
Intern
Joined: 25 Nov 2016
Posts: 21
Location: India
WE: Law (Non-Profit and Government)
Re: If the average (arithmetic mean) of a and b is 65 and the average (ari [#permalink]

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25 Dec 2017, 03:10
a+b=65*2=130
b+c=80*2=160
c-a=160-130=30
Ans is C
Manager
Joined: 24 Nov 2016
Posts: 151
Re: If the average (arithmetic mean) of a and b is 65 and the average (ari [#permalink]

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25 Dec 2017, 16:36
Bunuel wrote:
If the average (arithmetic mean) of a and b is 65 and the average (arithmetic mean) of b and c is 80, what is the value of c - a?

A. 90
B. 60
C. 30
D. 20
E. It cannot be determined from the information given.

$$Average=\frac{Sum}{Terms}$$

b and c: $$80=\frac{b+c}{2}$$, $$b+c=160$$
a and b: $$65=\frac{a+b}{2}$$, $$a+b=130$$

Subtract both equations to remove $$b$$ and find c minus a: $$b+c-(a+b)=160-130=30$$

Re: If the average (arithmetic mean) of a and b is 65 and the average (ari   [#permalink] 25 Dec 2017, 16:36
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