Question

how to find last term if n is not given but sum of numbers are given

Answer 1

if sum of the numbers is given then we can apply the formula an=n/2(a+l)
a= first term
l= last term

Answer 2

You can use this formula if-

a and d is given.

Firstly find n- ;

an=a+(n-1)d

Then,. Sn =n/2(a+l)