If the first term of an A.P. is 2 and common difference is 4, then the sum of its 40 terms is
Here a1= 2
D = common difference = 4
Sn = (2a + (n–1) d)
S40 = (2 x 2 + (39) 4)
= 20 (4 + 156)
= 3,200