Question

1 11. In an A.P., if a = 1, n = 20 and S. = 462, then n is
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Answer 1

Step-by-step explanation:

Correct option is C)

Hint:- The sum formula for up to 9 terms {Sn=2n{2a+(n−1)d} and the general term formula for n terms {an=a+(n−1)d} of an A.P. will be used along with the related terms.

Given:-

First term=a=1

nth term=an=20

Sn=399

Step 1: Using the general term formula to determine the relation of 'n' & 'd' for an=20

an=a+(n−1)d

Replacing the value of an=20

20=1+(n−1)d

Hence, the no. of term in the given A.P. for which the sum is 399 is 38.