The first and last terms of an A.P. are 1 and 11. If the sum of its terms is 36, then the number of terms will be
a1 = 1 (first term)
a11 = 11 = l (last term)
Sn= 36
But, Sn = 
(a + l)
36= 
(12)
n= 6
4
The first and last terms of an A.P. are 1 and 11. If the sum of its terms is 36, then the number of terms will be
a1 = 1 (first term)
a11 = 11 = l (last term)
Sn= 36
But, Sn = (a + l)
36= (12)
n= 6