Question

Find the sum of first 20 terms of the AP 5, 13, 21.


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Answer 1

Answer:

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Answer 2

Answer:

the sum of first 20 terms of given AP = 1620

Step-by-step explanation:

here, first term, a= 5

common difference, d= 8

now, formula of finding the sum of n terms are

s = (n/2) * (first term + nth term)

and nth term = first term + (n-1) common diff.

therefore,

20th term = 5 + (20-1)*8 = 157

and

sum of first 20 terms = (20/2) * (5+157) = 1620.