Question

Suppose $100 dollars is deposited into an account and the account doubles every 8 years . How much will in the account after 40years ?

Answer 1

yay, doubling time


the equation is
$A=P(2)^\frac{t}{d}$

A=final amount
P=initial amount
t=time elapsed in years
d=doubling time in years

ok

A=A
P=100
d=8yrs
t=40yrs

so

$A=100(2)^\frac{40}{8}$
$A=100(2)^5$
$A=100(32)$
$A=3200$


there will be $3200 in the account after 40 years

Answer 2

year 0   : D = $100
year 8   : D= $200
year 16 : D = $400
year 24 : D = $800
year 32 : D= $1600
year 40 : D= $3200

That's the longest way to do it :

40/8 = 5 ; the account is gonna doubles 5 times

$D(year40) = 100*2^{5} = 100*32 = 32000$