Question

In a. p if the 13th term is 13 and sum of first four terms is 24 find the sum of first 10 terms

Answer 1

o
a13= 13
s4= 24 , s10=?

s4=n/2 (2a+3d)
24=2(2a +3d)
12=2a+3d (i)


a + 12d=13 (ii)

subtracting i and ii
we get
21d= 14
d=1/2
a=7
then
s10= n/2 (2a+9d)
S10= 10/2 (2×7 + 9×1/2)
S10=10/2 (14 + 4.5)
S10 = 5× 18.5
s10 = 92.5


I hope it works
thanks