Q. 174.3( 10 Votes )

In an AP, if a = A. 19

B. 21

C. 38

D. 42

Answer :

Given


First term, a = 1,


Nth term, an = 20,


Some of n terms, Sn = 299


Using the formula



Where Sn = Sum of first n terms


n = no of terms


l = an = last term


2Sn = n(a + an)


2(399) = n(1 + 20)


n = 798/21


n = 38

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