Question

Question 5
The first term of an AP is 5, the last term is 45 and the sum is 400. Find the number of terms and the common difference.

Answer 1

Given that,
a = 5
l = 45
$S_n=400S_n=\frac{n}{2}(a+l)400=\frac{n}{2}(5+45)400=\frac{n}{2}\left(50\right)n=16l=a+(n-1)d45=5+(16-1)d40=15dd=\frac{40}{15}=\frac{8}{3}$