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M22-21

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M22-21  [#permalink]

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New post 16 Sep 2014, 01:17
00:00
A
B
C
D
E

Difficulty:

  15% (low)

Question Stats:

78% (01:02) correct 22% (01:16) wrong based on 144 sessions

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Math Expert
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Re M22-21  [#permalink]

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New post 16 Sep 2014, 01:17
Official Solution:


What is the value of

\(10-8+6-4+2-0+(-2)-(-4)+(-6)-(-8)+(-10)-(-12)+(-14)-(-16)+(-18)-(-20)\)?


A. 8
B. 10
C. 12
D. 14
E. 16


We should find the value of the following expression:

\(10-8+6-4+2-0+(-2)-(-4)+(-6)-(-8)+(-10)-(-12)+(-14)-(-16)+(-18)-(-20)\)

Notice that we have 8 pairs:

\(10-8=2\);

\(6-4=2\);

\(2-0=2\);

\((-2)-(-4)=2\);

\((-6)-(-8)=2\);

\((-10)-(-12)=2\);

\((-14)-(-16)=2\);

\((-18)-(-20)=2\);

So, the sum of each pair is 2, which makes the whole sum equal to \(8*2=16\).


Answer: E
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Re: M22-21  [#permalink]

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New post 03 Aug 2017, 07:44
1
The numbers from 10 to -10 get cancelled out.
So you have to simply add up 12-14+16-18+20
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Re: M22-21  [#permalink]

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New post 07 Mar 2018, 00:33
I don't understand the question ''What is the value of 10 - 8 + 6 - 4 + ... - (-20) ?
'' it can be evrything since .. is unknow?
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Re: M22-21  [#permalink]

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New post 07 Mar 2018, 02:12
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Re: M22-21  [#permalink]

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New post 10 Oct 2018, 10:58
Cancelling pairs out works the best for me: -2,2; -10;10, -8,8 etc. It leaves you with the last 5 numbers sum of which gives you 16.
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Re: M22-21   [#permalink] 10 Oct 2018, 10:58
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