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Programming
A Complete Problem
Thus far we have covered all of the operations possible in pro-
grams, 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 program-
ming using the following aids provided with your HP-65.
= HP-65 Program Form
= HP-65 User Instruction Form
= HP-65 Blank Magnetic Cards
= HP-65 Pocket Instruction Card
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 yourtotal savings earn 1% per month. By delaying pur-
chase of the house, the required downpayment increases through
inflation by 0.5% per month. Given these assumptions, answers
to the following questions are desired:
= What is the new required downpayment each and every
month?
= What are your total savings each month?
= Whatis the difference between savings and required down-
payment each month?
= When will you be able to purchase the house (assuming it
is still on the market)?
= What is the difference in a particular month (possibly to
see if a projected bonus could make it possible to pur-
chase earlier)?
To start, we will break this seemingly complex problem into man-
ageable 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 I, . . . , B each defined to pro-
vide one answer. We shall do this.
Label A: Given $4000 required downpayment increasing at
0.5% per month. What is the monthly total downpayment? 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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