Find the sum of first 22 terms of an AP in which d = 7 and 22nd term is 149.
d = 7 a22 = 149 S22 = ? an = a + (n − 1)d a22 = a + (22 − 1)d 149 = a + 21 × 7 149 = a + 147 a = 2 Sn = n/2 (a + an) = 22/2 (2 + 149) = 11 × 151 = 1661
