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Sample problems Solutions sections 2.3 & 2.4. 1) Your company estimates it will ... 3) You make monthly deposits of $100 into an annuity and after 30 years.
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cost of $800,000 in 5 years. To do this a sinking fund is established by
making equal monthly payments into an account paying 6.6% compounded
monthly. How much should each payment be? ($11,290.42)
60
mt
r
m
r
m
= โ = solving for P gives
compounded annually. Due to a change in employment, these deposits stop
after 10 years, but the account continues to earn interest until Betty
retires 25 years after the last deposit is made. How much is in the account
when Betty retires? ($143,785.10)
First determine the accumulation from the periodic deposits:
mt
r P m S r m
10
=. Now this amount earns
interest for 25 years compounded annually:
25
mt
r
m
wish to accumulate $160,000. What annual rate compounded monthly will be
required to do this? (0.083480405763)
Here in
mt
r P m S r m
= we sill solve for r:
360
r
r
r
$125 a month into a mutual fund that averages7.75% compounded monthly.
How many years will be needed to do this? (31.426831333098)
We need to solve
mt
r P m S r m
= for t.
12
t
t
monthly payments at 1.5% interest per month on the unpaid balance. How
much are your payments? ($51.05) What is the total interest paid? ($118.90)
Here we use the present value of an annuity formula:
mt
r P m V r m
โ
โ โ โ โ
18
โ
โ โ โ โ
The total interest is the total paid โ initial cost: 18(51.05)-800 = 118.90.
Determine the total interest paid for the loan in part (a) ($182,710.40) and
(b) ($82,382).
Interest (a): 993.64(360) โ 175000 = 182710.40.
Interest for (b): 1429.90(180)-175000 = 82382.
Suppose you have financed your home for 30 years. How much is the unpaid
balance after making payments for 20 years? ($91,557.55)
This unpaid balance forms another annuity. The present value of this annuity will
be the amount owed after making the 240
th payment.
mt
r P m V r m
โ โ โ โ โ
120
โ โ โ โ โ
Suppose before making the first payment you receive a raise and can pay an
extra $150 each month (30 year loan). How long will it take to pay off the
mortgage? (22.022274711642 years)
Instead of the regular payment of 993.64 we can pay 1143.64. Solving for t gives t
= 22.022274711642 years.
mt
r P m V r m
โ
โ โ โ โ
โ + โ (^) โ โ โ
โ โ โ โ โ โ
= โ
12
โ t
โ โ โ โ
โ + โ (^) โ โ โ
โ โ โ โ โ โ
=.
8.4% compounded monthly. If they decide to withdraw equal monthly
payments for 10 years, at the end of which time the account will have zero
balance, how much should they withdraw each month? ($2469.04)
mt
r P m V r m
โ
โ โ โ โ
120
โ
โ โ โ โ
annually. Mallory begins at age 20 and deposits $2000 a year till age 29, for
a total of 10 deposits, then does nothing till retirement at age 65 (36 years).
How much will Mallory have at age 65? Lauren begins at age 29 depositing $
a year until retirement at age 65 (37 deposits). How much will Lauren have at
retirement? (Mallory: $2,075,509.03) (Lauren: $1,087,197.38).
Mallory: First determine the accumulation of the 10 deposits.
mt
r P m A r m
10
= then this is compounded annually for
36 years โ A = 35097.47(1 + 0.12)
36
= 2,075,509.03.
Lauren:
mt
r P m A r m
37
Start saving early!!!!!!!!!!!!!!!!