Mary puts £1200 into an account where the annual rate of interest is 5∙5%. How long will it be before she has at least £1400 in her account?

FV = PV [1 + R]^N

1400 =1200[1 + 0.055]^N

1400 = 1200 x 1.055^N divide both sides by 1200

1.16667 =1.055^N Take the log of both sides

N =Log(1.16667) / Log(1.055)

N =2.879 years =~3 years.