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Question 13. Find the sum:(vii) 25 + 28 + 31 + . . . + 100

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This is an arithmetic progression based question from Chapter name- Arithmetic Progression
Chapter number- 9
Exercise – 9.6
In this question we have been given the arithmetic progression. Also we have to find the sum of it.

CBSE DHANPAT RAI PUBLICATIONS
Understanding CBSE Mathematics
Class :- 10th
Question no 13(vii)

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1 Answer

  1. Given series is an A.P. with first term(a) = 25,

    Common difference(d) = 28 − 25 = 3 and nth term(an) = 100.

    We know nth term of an A.P. is given by, an = a + (n − 1)d.

    => 100 = 25 + (n − 1)(3)

    => 100 = 25 + 3n − 3

    => n = 88/3

    => n = 26

    Also we know sum of n terms of an A.P. is given by Sn = n[a + an]/2.

    S26 = 26[25 + 100]/2

    = 13(125)

    = 1625

    Hence, the sum of terms of the given series is 1625.

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