interest

[palaniyapan]

Let's say I put $100 in the sterling pound.Assuming that ,I get a interest of 4% every year.How many will take for the amount to double?Furthermore,is there any formula for calculating that?Thank you and have a nice day.

[Gnu]

To calculate the interest after n years, the formula is 100*(1.04)^n.  If the interest rate was 4.5%, the formula would be 100*(1.045)^n.

To find out how long it would take to double, assuming the interest rate stayed the same, you need to solve the equation

100*(1.04)^n = 200

so (1.04)^n = 2

now you need to take logs of both sides, using the laws of logs

n log 1.04 = log 2

so n = log 2/log 1.04 = 0.30103/0.01703 = 17.7 years.