Combinations of Choices If there are n choices for one type and m choices for second type, then number of combinations for both types is the product of choices:n*m.
7 r8 J, v: A) ]' i Example:
4 I' \3 d7 B: ?" R# w( n; d$ K5 ?+ L If there are 3 kinds of breads to choose from and 4 kinds of meats, then we can make 3*4=12 different sandwiches.
/ g9 c9 p9 g/ g- P If an alphabet has 26 letters, then the number of possible 2 letter word is 26*26=676.All of them may not be vaild words.* b& p# l- D6 y+ g; {7 Y8 m' {6 \
Remember:" T1 l: j! u) U
Do not add the choices to get the total combinations
( S! T$ a9 _6 ~* n! S, g7 M8 s$ nThe product rule can be applied to more than two types of choices: if there are 3 kinds of breads, 4 kinds of meats, and 6 kinds of cheeses, then we can make 3*4*6=72 different sandwiches. |
发表于 2012-8-15 12:55:17
