Question

find the sum of the 10th and 12th terms from the end of the A.P 4,9,14,....,89.

Answer 1

A10 =a +(n-1)d
= 89+(9)-5
= 89-45
= 44
A12= a+(11)d
= 89+(11)-5
= 89-55
= 34
now a10+a12=
= 44+34=78
ans : 78