You know that in continuous compounding, the future value of a current lump sum (of money) is compounded as: FV=PV*e Rn, with R the annualized interest rate and n the number of years. Now suppose you win a lottery that gives you 1 million dollars. But you can either get it now or pay 50% tax (i.e. Get 500,000 only) or get it in 10 years and pay 30% tax (i.e. Get $ 700,000 in 10 years), which one will you choose? Why? The interest rate is 4%