HP HP-15C

47
Section 4
Statistics Functions
A word about the statistics functions: their use is based on an understanding
of memory stack operation (Section 3). You will find that order of entry is
important for most statistics calculations.
Probability Calculations
The input for permutation and combination calculations is restricted to
nonnegative integers. Enter the y-value before the x-value. These functions,
like the arithmetic operators, cause the stack to drop as the result is placed
in the X-register.
Permutations. Pressing ´p calculates the number of possible
different arrangements of y different items taken in quantities of x items at a
time. No item occurs more than once in an arrangement, and different
orders of the same x items in an arrangement are counted separately. The
formula is
)!(
!
,
xy
y
P
xy


Combinations. Pressing |c calculates the number of possible sets
of y different items taken in quantities of x items at a time. No item occurs
more than once in a set, and different orders of the same x items in a set are
not counted separately. The formula is
)!(!
!
,
xyx
y
C
xy


Examples: How many different arrangements are possible of five pictures
which can be hung on the wall three at a time?
Keystrokes
Display
5 v 3
3
Five (y) pictures put up three (x) at a
time.
´p
60.0000
Sixty different arrangement possible.