Question

How many terms of the AP 25,28,31,...... must be added to get the sum 1625?

Answer 1

ANSWER

n=26

EXPLANATION

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

1625=n/2(50+3n-3)

3250=3n^2+47n

3n^2+125n-78n-3250=0

n(3n+125) - 26(3n+125)

n=26,-125/3

since n cannot be negative

therefore n=26