Q1 of 69 Page 78

Choose the correct alternative answer for each of the following sub questions.

15, 10, 5, . . . In this A.P. sum of first 10 terms is . . .

First term a = 15

Second term t1 = 10


Third term t2 = 5


Common difference d = t2 – t1 = 5 – 10 = – 5


No. of terms n = 10


Thus, By using sum of nth term of an A.P. we will find it’s sum



Where, n = no. of terms


a = first term


d = common difference


Sn = sum of n terms


We need to find S10



⇒S10 = 5 [ 30 + 9 × ( – 5)]


⇒S10 = 5 [ 30 – 45]


⇒S10 = 5 × ( – 15) = – 75


Hence, correct answer is (A)

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