Question

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

Answer 1

an = a + (n-1) d
350 = 17 + 9n - 9
9n = 342
n = 342/9
n = 38th term.

Sn = n/2 (a+an)
= 19 (17 + 350)
= 19 (367)
= 6973.

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Answer 2

a=17 an=350 d=9 n=?
we know that
an=a+(n-1)d
350=17+(n-1)9
350-17=(n-1)9
333/9=n-1
37=n-1
n=38
Sn=n/2(a+an)
Sn=19×(17+350)
Sn=19×367
Sn=6973...@ns