Question

Find the sum of the A.P: 3 + 15 + 27 + ...... + 231.

Answer 1

Answer:

Sn=2340

Step-by-step explanation:

a=3, d=15-3=12, An=231

An=a+(n-1)d

231=3+(n-1)12

231=3+12n-12

231=12n-12+3

231=12n-9

12n=231+9

12n=240

n=240/12

n=20

Sn=n/2(a+An)

S20=20/2(3+231)

S20=20/2×234

S20=10×234

S20=2340

Answer 2

3 + 15 + 27 + 65 + 231

answer is 65