Let the total amount that Sarah deposited be $x
using the annuity formula:
A=P[((1+r)^n-1)/r]
A=future value
r=rate
n=number of years
from the information given:
A=$500000
r=2.75%
n=65-42=23 years
p=$x
thus plugging our values in the formula we get:
500000=x[((1+0.0275)^(23)-1)/(0.0275)]
500000=31.50x
x=15,872.04883
She deposited 15,873.04883 per year
The monthly deposit will therefore be:
15873.04883/12=$1322.67
<span>Compound
interest formula</span>

Where
<span>
A= Future value
P =
the Principal (the initial amount of money)
r = annual interest rate</span>
t = time
<span>n=
number of times compounded in one t
Remark
----------------------------------------------------------------------------------
r is generally a percentage like 3%, 7% etc and
are applied in the formula as 0.03, 0.07...,
the interest is compounded generally annually (
n=1), quarterly (
n=4),
monthly (
n=12), etc...
t is in years,
In our problem:
</span>
A= 30 000
P =20 000
r = 15%=0.15
time = t = ?
n= 4
applying the formula:



75% of 12 months is 3/4 of 12 months, which is 9 months
Answer: 2 years, 9 months