A certain sum at simple interest amounts to Rs.1350 in 5 years and to Rs.1620 in 8 years. What is the sum?
SI = PRT/100 and Amount, A = P + SI
SI = A - P
A - P = PRT/100
In 5 years, 1350 - P = P*R*5/100
In 8 years, 1620 - P = P*R*8/100
Divide both equations,
(1350 - P)/(1620 - P) = 5/8
10800 - 8P = 8100 - 5P
P = 900
The correct option is A.