Question

a country's population in 1990 was 134 million. in 2000 it was a 139 million. estimate the population in 2014 using the exponential growth formula. round to the nearest million

Answer 1

f=ir^t

139=134r^10

139/134=r^10

r=(139/134)^(1/10) then:

f=134(139/134)^(t/10) so in 2014, t=24 so

f=134(139/134)^(2.4)

f≈146 million (to nearest million)

Some will say that you have to use the exponential function, but it really gives you the same answer...even for continuous compounding :)...

A=Pe^(kt)

139=134e^(10k)

139/134=e^(10k)

ln(139/134)=10k

k=ln(139/134)/10 so

A=134e^(t*ln(139/134)/10) when t=24

A=134e^(2.4*ln(139/134))

A≈146 million (to nearest million)

The only real reason or advantage to using A=Pe^(kt) is when you start getting into differential equations...