Question

The 13th term of an ap is four times its 3rd term. if the fifth term is 16 then find the sum of its first ten terms.

Answer 1

n=13
here a13=4a4
a5=15
a+(5-1)d=15
a+4d=15
again
a+12d=4a+12d
that implies a=0
then
d=15/4
a2=0+15/4=15/4
by that we find the ap
and we apply it on
the formula of sum by writing n=10
hope it helps you