Question

11. The sum of the first five terms of an AP is 55 and sum of the first ten terms of this AP is 235, find the sum of first 20 terms​

Answer 1

Answer:

given, (5/2)(2a+4d)=55

a+2d=11

and

5(2a+9d)=235

2a+9d=47

d=5 and a=1.

sum of first 20 terms

=10(2a+19d)

=10(2+95)

=970.

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