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Ymorist [56]
3 years ago
13

Find the number of terms, n, of the arithmetic series given a = 21, an = 39, and Sn = 210.

History
1 answer:
LekaFEV [45]3 years ago
6 0

The number of terms n is 7.

<u>Explanation:</u>

Given that:

First term a=21

nth term a_{n}=39

Sum up to n terms S_{n}=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

S_{n} =\frac{n}{2} (a+a_{n} )

Solution:

S_{n} =\frac{n}{2} (a+a_{n} )\\\\210=\frac{n}{2}(21+39)\\\\210=\frac{n}{2}(60)=30n\\\\n=210/30=7

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

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