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What is the sum of all the integers from 90 to 920 that end in 7?

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What is the sum of all the integers from 90 to 920 that end in 7?  [#permalink]

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New post 02 Dec 2019, 01:23
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  55% (hard)

Question Stats:

57% (01:59) correct 43% (02:19) wrong based on 35 sessions

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Joined: 25 Jan 2019
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Location: India
Schools: ISB '21
Re: What is the sum of all the integers from 90 to 920 that end in 7?  [#permalink]

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New post 02 Dec 2019, 01:41
1
First Term :97
Since, the integers end in 7, the common difference would be 10.
Last Term: 917

Total Number of Terms : (n)

917=97+(n-1)10
Solving, n=83

Sum of all integers between 90 and 920: (83*(97+917))/2 = 42081

Option (b)
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Re: What is the sum of all the integers from 90 to 920 that end in 7?  [#permalink]

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New post 02 Dec 2019, 02:26
1. Numbers ending in 7 are 97, 107,117,127, ..., 917. The sequence comes out to be an Arithmetic progression with the common difference(d) as 10.
2. Using the formula (a)n= a1 + (n-1)d , we can determine the number n which comes out to be 83. {917=97+ (n-1)10 }
3. 83 can be used to find the sum of AP. Sum= (83/3)* ( 97+917) = 42,081

Option B
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Re: What is the sum of all the integers from 90 to 920 that end in 7?   [#permalink] 02 Dec 2019, 02:26
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What is the sum of all the integers from 90 to 920 that end in 7?

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