Question

the first and last term of an ap are 5 and 45 respectively . if the sum of all its term is 400 , finds its common difference.

Answer 1

Sn =n/2(t1+tn)
400=n/2(5+45)
400=n/2(50)
400/25=n
n=16
Tn=a+(n-1)d
45=5+(16-1)d
45-5=15d
40/15=d
8/3=d
d=2.66