HP HP-67

88 Function Keys
Example: In an electrical circuit, four resistors are connected in
parallel. Their values are 220 ohms, 560 ohms, 1.2 kilohms, and 5
kilohms. What is the total resistance of the circuit?
1
RT =
1 + 1 + 1 + 1
R, R, Ry R,
_ 1
1 1 1 1
+ + +
220 560 1200 5000
Press Display
22009 4.545454545-03
560 03 1.785714286-03
0.01
1200 @
oot
5000
[0.01 Sum of reciprocals.
Q m The reciprocal of the sum
of the reciprocals yields
the answer in ohms.
Factorials
The (N (factorial) key permits you to handle permutations and
combinations with ease. To calculate the factorial of a positive integer
in the displayed X-register, press 03 (N!].
Example: Calculate the number of ways that six people can line up
for a photograph.
Method: P§ = 6! =6 X5 X4 X3 X2 X1,
Press Display
6
o N 720.00 The answer.
The calculator overflows for factorials of numbers greater than 69.