Question

The first twrm of an ap.is 5 and its last term is 45 of sum of all term is 125 then how many terms are ther in tht ap

Answer 1

a=5,An=45,Sn=125
An=a+(n-1)d
45=5+(n-1)d
40=(n-1)d

Sn=n/2(2a+(n-1)d)
125=n/2(10+(n-1)d)
125=n/2(10+40)
125=25n
n=5
Therefore,no of terms=5