Q. 124.8( 13 Votes )

The first term of

Answer :

First term of AP, a = 5

Let no of terms be 'n' and common difference is 'd'

Last term of AP, an = 45

Given, sum of n terms = 400

And we know, sum of an AP if first term(a) and last term(an) is given,

Putting the values, we get,

800 = 50n

n = 16

i.e. 16 terms are there and 16th term is last and equal to 45

Also, we know,

nth term of an AP,

Where, a and d are first term and common difference, respectively.

As, a16 = 45

a + 15d = 45

5 + 15d = 45

15d = 40

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