Question

How do I solve this problem?

Answer 1

6480.

Explanation:

This is an arithmetic series with first term 2, last term 160 and common difference 2.

Sum = n/2 [ a1 + L)

= (80/2)(2 + 160)

= 40 * 162

= 6480.

Answer 2

3240

Explanation:

Sum=n/2(2a+(n-1)d)

=80/2(2*1+(80-1)1)

=40(2+79)

=40*81

=3240