Explanation:
FV = PV (1+i)^n is the compounding formula to show the final amount in the account after three years with i = .10 n = 3
the interest would be this amount - the original PV
331 = PV ( 1 +.1)^3 - PV
331 = PV ((1+.1)^3 -1)
shows PV = 1000 Rupees