HP 20b Business Consultant Manual

hp calculators
HP 20b
Using Memories to Solve Problems
Constant memory and planning
Memory registers
Other memory locations
Understanding register arithmetic
Viewing register contents
Clearing memories
Practice using registers to solve problems

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Constant memory and planning
Because of the HP 20b Constant Memory feature, any current computations may be stopped at any moment for later
resumption without any data loss. In the HP 20b, memory is organized as a set of registers, where each register can
hold a number representation of any positive or negative value with a 12-digit mantissa and a three-digit integer, positive
or negative exponent of ten.
Memory registers
There are 10 data storage registers in the HP 20b calculator. These registers can be directly addressed anytime it is
necessary, provided that the register is available. Special care must be taken in regard to make sure that the chosen
register isn’t being used for other purposes. As a general rule, two basic operations can always be performed over
existing register contents: storing and retrieving (or recalling) numbers.
Assuming that the display contains a value to be stored, to store that number in a register, press :$ and then a
number key from 0 to 9. To retrieve the information stored in one of the registers back to the display and use it in further
calculations, press Land then a number key from 0 to 9.
It is also possible to store and recall values directly into the five Time Value of Money (TVM) registers, N, Y, V,
M, and Fby pressing :$ and then one of these keys. Values in these registers are recalled for viewing or
further use by pressing and then Lone of these keys. If you are not planning to solve a TVM problem, then these five
locations can be used as extra storage registers.
Other memory locations
The HP 20b also has memory space allocated to store statistical data and cash flow data. There is room in the HP 20b
to store a total of 50 statistical data pairs or 50 cash flow values and frequencies, or any mixture of the two, provided
there are 50 or fewer total pairs. If you were to store one statistics data pair, you would then have room for 49 distinct
cash flows, for example. These memory locations are not covered in this learning module, as they are discussed
elsewhere.
Example 1: The index for conversion between American Dollars and Euros is stipulated as 1.00 Euro = US$1.59.
Which keystroke sequence stores this index in register R1?
Solution: The complete sequence for typing the index in and storing its value in register R1is:
1.59:$1
Understanding register arithmetic
Along with storing and retrieval, you can use storage register arithmetic and recall register arithmetic on the ten memory
registers. The next example shows how this would work for storage register arithmetic.
Example 2: The index for conversion between American Dollars and Euros has its valued raised by 1%. What is the
keystroke sequence that updates the index in register R1?
Solution: When the keystrokes below are used, the index is updated in R1.

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1.01:$*1
These keystrokes will multiply the value in the display, 1.01, by the value stored in memory register 1 and
store the result in register 1. If it is necessary to check the resulting value stored in R1or use it in further
calculations, the following keystroke sequence must be used to bring its contents to the display:
L1
Answer: Now the relationship is set to 1.00 Euro = US$1.61. The value displayed is the updated index value. Note
that the actual value displayed will vary depending on your choice of the number of decimal places
displayed. The full value is 1.6059.
The next example shows how recall register arithmetic works. In chain or algebraic mode, you must press = to finish
the sequence. In RPN mode, this keystroke is not necessary.
Example 3: Store 123 in R2and the multiply the following numbers by the value stored in it: 3, 10, and 14. Use recall
register arithmetic.
Solution: First, store 123 in memory 2.
1.23:$2
Then, to multiply the first number 3 by the contents of memory 2, press
3L*2= (In RPN mode, there is no need to press =)
Then, to multiply the second number 10 by the contents of memory 2, press
10L*2= (In RPN mode, there is no need to press =)
Then, to multiply the third number 14 by the contents of memory 2, press
14L*2= (In RPN mode, there is no need to press =)
Answer: The values displayed would be 369, 1230 and 1772.
For store or recall register arithmetic, any of the four arithmetic operators can be used: +, -, *, or /.
Viewing register contents
To view the contents of a memory register, you can, of course, recall it to the display if you wish. However, this may
disrupt the stack or an operation in progress. Another way to view the data registers is to press :t. This key
sequence will display the contents of memory 1 as shown below.

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Figure 1
This screen indicates that memory 1 has the value of 0.00 presently stored in it. You can press < or > to scroll
through the ten memory registers. Note as well that INPUT is active in the top right of the display. This indicates that if
you key in a value and press I, that value will be stored into the memory register displayed, replacing any value
previously stored there.
If you press < or > enough times, you will eventually see, in addition to the contents of memories 0 through 9,
menu options reporting how many of the available 50 slots for cash flow and statistical data values remain, as well as the
number of statistical data values presently stored and the number of cash flow values stored.
Clearing memories
To clear all data memories at once, press :x. and then < or >until you see the display shown below in
figure 2. At this display, pressing Iwill reset all ten data memories to a value of 0. The message “Memory Reset”
will be scrolled across the screen.
Figure 2
Practice using registers to solve problems
Example 4: The sales price of the last 10 homes sold in the Parkdale community were: $198,000; $185,000;
$205,200; $225,300; $206,700; $201,850; $200,000; $189,000; $192,100; $200,400. What is the average
of these sales prices?
Solution: Register R0will be used to perform all operations. Then the resulting value will be brought back to the
display. The average is computed using the following expression,
n
d
xn
∑
=Figure 3
In this example, nis 10 (ten) and dnis each sales price. So, all values are accumulated in R0and then the
average is obtained by dividing the total accumulated by the number of entries. Be sure to initialize the
contents of R0before starting the problem:
0:$0
Now, each sales price is typed in and added to the existing amount in R0:
198000:$+0

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The second sales price is entered by pressing:
185000 :$+0
Be sure to key in all sales prices and press :$+0. When the last sales price is keyed in and
accumulated, its value remains in the display:
205200:$+0 225300:$+0
206700:$+0 201850:$+0
200000:$+0 189000:$+0
192100:$+0 200400:$+0
Now, divide R0(the accumulated sales) by ten.
10:$/0
At this point, R0contains the resulting value: the average sales price for homes sold in Parkdale
community. To display this average, press:
L0
Answer: The average sales price for homes sold in Parkdale community is $ 200,355.00. Of course, this problem is
probably more efficiently solved using the statistics data registers and functions, which are described in
another learning module, but it does illustrate how memories may be used.