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A Complete Problem
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Thus far we have covered all of the operations possible in programs, illustrating them with small,
individual examples. In the real world, things are not quite so simple. Consequently, we present
a real problem and will take you through the programming using the following aids provided with
your HP-65.
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HP-65 Program Form
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HP-65 User Instruction Form
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HP-65 Blank Magnetic Cards
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HP-65 Pocket Instruction Card
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Assume that you need $4000 to make a downpayment on a house and your current savings are $2000.
Assume further that you are able to add the amount of $185 to your savings monthly and that your
total savings earn 1% per month. By delaying purchase of the house, the required downpayment
increases through inflation by 0.5% per month. Given these assumptions, answers to the following
questions are desired:
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What is the new required downpayment each and every month?
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What are your total savings each month?
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What is the difference between savings and required downpayment each month?
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When will you be able to purchase the house (assuming it is still on the market)?
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What is the difference in a particular month (possibly to see if a projected bonus could
make it possible to purchase earlier)?
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To start, we will break this seemingly complex problem into manageable pieces and, following the steps
outlined at the beginning of this section, create a program to give us the desired answers. Conveniently,
there are five answers desired. One way to look at the problem is to have keys  A, . . . , E
each defined to provide one answer. We shall do this.
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Label A: Given $4000 required downpayment increasing at 0.5% per month. What is the monthly total
downpaymcnt? You may recall that this problem is that of calculating a monthly compound growth schedule
with a growth (inflation) factor of 1.005.
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