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.
Here, a = 17, l = 350, d = 9
We know that,
l = a + (n - 1)d
350 = 17 + (n -1) x 9
350 -17 = 9 x (n - 1)
333 = 9 x (n -1)
n - 1 =
n = 37 + 1 = 38
Hence, there are 28 terms.
= 19 x 367 = 6973.