# Chapter 15 - Probability Distributions; The Mth/probability.. Sub-menu - Part 1; Factorials, Combinations, And Permutations - HP 50g User Manual

Graphing calculator.

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
P
n
Also, the number of combinations of n objects taken r at a time is
n
⎜ ⎜
⎟ ⎟
r
We can calculate combinations, permutations, and factorials with functions
COMB, PERM, and ! from the MTH/PROBABILITY.. sub-menu.
operation of those functions is described next:
• COMB(n,r): Calculates the number of combinations of n items taken r at
a time
Page 15-1
n
(
n
1
)(
n
1
)...(
r
n
(
n
1
)(
n
2
)...(
r
!
n
r
) 1
n
/( !
n
n
r
) 1
r
( !
n
r
)!
n
!
r
)!
The  