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Page 15-1
Chapter 15
Probability Distributions
In this Chapter we provide examples of applications of the pre-defined
probability distributions in the calculator.
The MTH/PROBABILITY.. sub-menu - part 1
The MTH/PROBABILITY.. sub-menu is accessible through the keystroke
sequence
„´. With system flag 117 set to CHOOSE boxes, the
following functions are available in the PROBABILITY.. menu:
In this section we discuss functions COMB, PERM, ! (factorial), and RAND.
Factorials, combinations, and permutations
The factorial of an integer n is defined as: n! = n⋅ (n-1) ⋅ (n-2)…3⋅2⋅1. By
definition, 0! = 1.
Factorials are used in the calculation of the number of permutations and
combinations of objects. For example, the
number of permutations of r
objects from a set of n distinct objects is
Also, the number of combinations of n objects taken r at a time is
We can calculate combinations, permutations, and factorials with functions
COMB, PERM, and ! from the MTH/PROBABILITY.. sub-menu. The
operation of those functions is described next:
• COMB(n,r): Calculates the number of combinations of n items taken r at
a time
)!/(!)1)...(1)(1( rnnrnnnn
rn
P −=+−−−=
)!(!
!
!
)1)...(2)(1(
rnr
n
r
rnnnn
r
n
−
=
+−−−
=
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SG49A.book Page 1 Friday, September 16, 2005 1:31 PM