The first and the last terms of an AP are 17 and 350 respectively. If the common difference is 9, then find the number of terms in the AP and their sum.
38; 6973
Given,
First term =a=17
Last term =l=350
Common difference =d=9
Using formula an=a+(n−1)d, we can say that
350=17+(n−1)(9)
⇒350=17+9n−9
⇒342=9n
⇒n=3429=38
Applying formula, Sn=n2(2a+(n−1)d), we get
S38=382(34+(38−1)9)
⇒S38=19(34+333)=6973
Therefore, there are 38 terms and their sum is equal to 6973.