Question

In an A.P the first term is -5 and the last term is 45. if the sum of all numbers in the A.P is 120, then how many terms are there? what is the common difference?

Answer 1

Answer:

Here the number of terms for all nth terms of m AP series is =m

First term of the series ⇒ a=n

The common difference of the series

d=(2n−1)−n=n−1

So applying formula

S=2m(2n+(m−1)(n−1))

S=2m(2n+mn−m−n+1)

S=2m(mn−m+n+1)

Hence, this is the answer.