Question

Let anan be an arithmetic progression, for which a1=15a1=15 and d=3d=3. Find the sum of the first 10 elements.

Answer 1

Hey there,

a1 = 15
d = 3

Sn = n/2[2a + (n-1)d]

Sn = 10/2[2(15) + (10-1)3]
Sn = 5[30 + 9(3)]
Sn = 5[30 + 27]
Sn = 5[57]
Sn = 285

Hope it helps :)