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# The Operation ==> is defined by x ==>y=x+(x+1)+(x+2)... +y.

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Intern
Joined: 25 Oct 2012
Posts: 5
The Operation ==> is defined by x ==>y=x+(x+1)+(x+2)... +y.  [#permalink]

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Updated on: 20 Nov 2012, 03:17
1
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Question Stats:

100% (01:55) correct 0% (00:00) wrong based on 13 sessions

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The Operation ==> is defined by x ==>y=x+(x+1)+(x+2)... +y. For Example 3==>7=3+4+5+6+7. What is the value of (100==>150) - (125==>150)?

Hi,

I´ve been working through the Mgmat books and am currently working on Consecutive Integers where I stumbled on the following problem.
Even with the solution I have no Idead whats happening.

Well I assumed I can´t simply plug in the values as this would be very time consuming.

Any chance someone could explain this to me step by step?

Thank you very much in Advance!!

Originally posted by Donnie on 20 Nov 2012, 02:52.
Last edited by Bunuel on 20 Nov 2012, 03:17, edited 1 time in total.
Renamed the topic.
Director
Status: Done with formalities.. and back..
Joined: 15 Sep 2012
Posts: 559
Location: India
Concentration: Strategy, General Management
Schools: Olin - Wash U - Class of 2015
WE: Information Technology (Computer Software)
Re: Consecutive Integers Operation (-->) is defined by x-->y ...  [#permalink]

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20 Nov 2012, 03:11
4
Donnie wrote:
Hi,

I´ve been working through the Mgmat books and am currently working on Consecutive Integers where I stumbled on the following problem.
Even with the solution I have no Idead whats happening.
Q. The Operation ==> is defined by x ==>y=x+(x+1)+(x+2)... +y. For Example 3==>7=3+4+5+6+7.
What is the value of (100==>150) - (125==>150)?
Well I assumed I can´t simply plug in the values as this would be very time consuming.
Any chance someone could explain this to me step by step?
Thank you very much in Advance!!

Since function is defined as: x ==>y=x+(x+1)+(x+2)... +y
hence,
(100==>150) - (125==>150)
= (100+101+....+149+150) - (125+126+..... 150)
= (100 +101+....+123+124)
[Second list(125..150) is subset of first list(100..150), hence each term of second list gets cancelled from corresponding item from first list. And only items 101.. 124 remain in list 1]
= (100+124)/2 *25
[Avg of first and last * total number of terms]
= 2800

Hope it helps.
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Joined: 09 Sep 2013
Posts: 13742
Re: The Operation ==> is defined by x ==>y=x+(x+1)+(x+2)... +y.  [#permalink]

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20 Oct 2019, 08:18
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Re: The Operation ==> is defined by x ==>y=x+(x+1)+(x+2)... +y.   [#permalink] 20 Oct 2019, 08:18
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