Question

If the sum of first ten term of snaps is 100 & sum of the first twenty term of an AP is 400. Find the sum of first twenty five terms ​

Answer 1

2a+9d=20

2a+19d=40

d=2

d=2 in eq1

a=1

S25=675

Answer 2

Answer:

Step-by-step explanation:

Here sum of ten terms is given that 100 . It means that S10=100 here n=10. So 10/2(2a+(10-1)d=100 and now. By solving it we get. 2a+9d=20 ...........(1) and sum of twenty terms is 400 it means that S20=400 and n=20 so 20/2(2a+19d)=400 so. 2a+19d=40 .........(2) and by solving (1)and(2) we get d=2 and by putting the value of d in (1) we get a=1 and now S25=25/2(2a+24d)

and by substituting the value of a and d in it we get S25=625 so sum of twenty five terms is 625