This is the basic and conceptual question from Chapter name- Arithmetic Progression
Chapter number- 9
Exercise 9.6
In this question we have been given an arithmetic progression. And we have to find its sum.
CBSE DHANPAT RAI publications
Class:- 10th
Solutions of CBSE Mathematics
Question 13(v)
Given series is an A.P. with first term(a) = 7,
Common difference(d) = 101/2 − 7 = (21 − 14)/2 = 7/2 and nth term(an) = 84.
We know nth term of an A.P. is given by, an = a + (n − 1)d.
=> 84 = 7 + (n − 1)(7/2)
=> 168 = 14 + 7n − 7
=> n = 161/7
=> n = 23
Also we know sum of n terms of an A.P. is given by Sn = n[a + an]/2.
S23 = 23[7 + 84]/2
= 23(91)/2
= 2093/2 = 1046.5
Hence, the sum of terms of the given series is 1046.5