# The sum of n terms of an A.P. is . Find its 20th term.

Taking n = 1, we get

S1 = 4

a1 = 4

Taking n = 2, we get

S2 = 13

a2 = S2 – S1 = 13 – 4 = 9

Taking n = 3, we get

S3 = 27

a3 = S3 – S2 = 27 – 13 = 14

So, a = 4,

d = a2 – a1 = 9 – 4 = 5

Now, we have to find the 20th term

an = a + (n – 1)d

a20 = 4 + (20 – 1)5

a20 = 4 + 19 × 5

a20 = 4 + 95

a20 = 99

Hence, the 20th term is 99.

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