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

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

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New post 20 Nov 2012, 02:52
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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!!

Last edited by Bunuel on 20 Nov 2012, 03:17, edited 1 time in total.
Renamed the topic.

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Re: Consecutive Integers Operation (-->) is defined by x-->y ... [#permalink]

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New post 20 Nov 2012, 03:11
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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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Re: The Operation ==> is defined by x ==>y=x+(x+1)+(x+2)... +y. [#permalink]

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New post 30 Sep 2017, 09:11
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Re: The Operation ==> is defined by x ==>y=x+(x+1)+(x+2)... +y.   [#permalink] 30 Sep 2017, 09:11
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