The first term of an AP is 5, the last term is 45 and the sum is 400. Find the number of termsand the common difference.
We can calculate the sum of N number of terms as :
400 
800 = 
(5 + 45)
50
n = 16
Now, common difference can be calculated as follows:
an = a + (n – 1)d
45 = 5 + 15d
15d = 40
d = 40/15 = 8/3
Hence, n = 16 and d = 8/3
16