The first and last terms of an AP are 1 and 11 respectively. If the sum of its terms is 36, find the number of terms.

Given: the sum of its terms is 36, the first and last terms of an AP are 1 and
11.
To find: the number of terms
Sum of AP using first and last terms is given by

36 × 2 = n (1 + 11)
n = 6