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.

Question

Philoid · Accepted Answer

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:

a_n = a + (n – 1)d

45 = 5 + 15d

15d = 40

d = 40/15 = 8/3

Hence, n = 16 and d = 8/3