9514 1404 393
Answer:
- $250,000 house price. $50,000 down payment
- 2 years, 3% from the bank, monthly: $2024.06
- 5% APR, 30 years, monthly: 1073.64
Explanation:
1. House prices vary considerably. In January, 2021, the median US house price was about $269,000, growing at the rate of about 3.2% per year. For the purpose of this problem, we have chosen a slightly lower price of ...
$250,000 . . . selected house price
20% of this price is ...
0.20 × $250,000 = $50,000 . . . amount of down payment
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2. House prices are growing faster than the interest rate we can get at the bank, so we want to minimize the amount of time we save for a down payment. At the same time, we recognize that saving this amount quickly will put a significant strain on the budget. We choose a period of 2 years, and assume a bank rate on savings of 3%. (US rates in mid-2021 average about 0.04%.) This annuity formula gives the future value of a series of payments:
A = P((1+r/12)^(12t)-1)(12/r) . . . . monthly payment P at annual rate r for t years
Solving for P, we have ...
P = A(r/12)/((1 +r/12)^(12t) -1)
Filling in the chosen numbers, we find we need to save ...
P = $50,000(0.03/12)/(1 +0.03/12)^(12·2) -1) = $50,000(0.0025)/0.06175704
P = $2024.06
$2024.06 needs to be deposited every month for 2 years at 3%.
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3. The mortgage will be for ...
$250,000 -50,000 = $200,000
We assume we can get an APR of 5% on a 30-year loan. (US rates in mid-2021 are around 3.2%.) The formula for the payment amount is ...
A = P(r/12)/(1 -(1 +r/12)^(-12t)) . . . principal P at rate r for t years
Filling in the chosen numbers, we find the monthly payment to be ...
A = $200,000(0.05/12)/(1 -(1 +0.05/12)^(-12·30))
= $200,000(0.0041666667)/0.77617340 = $1073.64
The monthly mortgage payment will be $1073.64.