Find the number of terms, n, of the arithmetic series given a = 21, an = 39, and Sn = 210.
A.7
B. 8
C. 9
D.5

The number of terms n is 7.

Explanation:

Given that:

First term a=21

nth term =39

Sum up to n terms =210

To Find:

The number of terms n in the arithmetic progression.

Formula to be used:

Sum up to n terms Sn is given by the expression

Solution:

Number of terms n in the given series is n=7

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