Question

20, 21 ,22,23 with solutions

Answer 1

Answer:

Step-by-step explanation:

21. Given ,

1st term is 5 and 3rd term is 15 then , a=5 and a+2d = 15

Solving the equations we get d=5

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

= 16/2 (2 (5) + (15)5)

=680