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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