Question

Find number of terms in AP whose first and last term are 12 and 8 respectively and sum of all the terms is 120.

Answer 1

a=12, l=8, Sum=120, n=?
sum=n/2(a+l)
120=n/2(12+8)
120=n/2(20)
20n=240
n=240/20
n=12
no. of terms=12