Q. 64.3( 168 Votes )

# The first and the last terms of an AP are 17 and 350 respectively. If the common differenceis 9, how many terms are there and what is their sum?

We have;
First term, a = 17,
Last term, an = 350 and
Common difference, d = 9

We know, nth term formula:

an = a + (n – 1)d

350 = 17 + (n – 1)9

(n – 1)9 = 350 – 17

n – 1 = 333/9 = 37

n = 38

and we know, sum of 'n' terms of an AP if first and last term is given is

= 19*367

= 6973

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