week 2
1
Basic Combinatorics
• Multiplication Principle
Suppose we are to make a series of decisions. Suppose there are
c
1
choices for decision 1 and for each of these there are
c
2
choices for
decision 2 etc. Then the number of ways the series of decisions can
be made is
c
1
·
c
2
·
c
3
···.
•
Example 1
:
Suppose I need to choose an outfit for tomorrow and I have 2 pairs
of jeans to choose from, 3 shirts and 2 pairs of shoes that matches
with these shirts. Then I have 2·3·2 = 12 different outfits.

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