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Find the sum of last ten terms of the AP...

Find the sum of last ten terms of the AP `8`, `10`, `12`, …, `126`.

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For finding, the sum of last ten terms, we write the given AP in reverse order.
i.e., `126, 124, 122, …, 12, 10, 8`
Here, first term (a) = 126, common difference, (d)`=124 - 126= -2`
` :. S_(10)=(10)/(2)[2a+(10-1)d] " " [:' S_(n)=(n)/(2)[2a+(n-1)d]]`
` " " =5{2(126)+9(-2)}=5(252-18)`
` " " =5xx234=1170`
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NCERT EXEMPLAR ENGLISH-ARITHMETIC PROGRESSIONS-Short Answer Type Questions
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  2. Which term of the AP 53, 48, 43, … is the first negative term ?

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  3. How many numbers lie between 10 and 300, which divided by 4 leave a re...

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  11. If S(n) denotes the sum of first n terms of an AP, then prove that S(1...

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  12. Find the sum of first 17 terms of an AP whose 4th and 9th terms are -1...

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  13. If sum of first 6 terms of an AP is 36 and that of the first 16 terms ...

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  14. Find the sum of all the 11 terms of an AP whose middle most term is 30...

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  15. Find the sum of last ten terms of the AP 8, 10, 12, …, 126.

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  16. Find the sum of first seven numbers which are multiples of 2 as well a...

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  17. How many terms of the AP -15, -13, -11, … are needed to make the sum ...

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  18. The sum of the first n terms of an AP whose first term is 8 and the co...

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