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.0 f7 H; ~+ p5 g1 n3 _6 G" l7 b
Example:
& m$ D W: _) j9 O* p3 z If there are 3 kinds of breads to choose from and 4 kinds of meats, then we can make 3*4=12 different sandwiches.+ O! J4 L. Q% Y( j: ]8 o
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.8 b! @/ ~5 B. ]9 { f) ^, T+ [
Remember:
1 e8 R. X! [4 Q% O Do not add the choices to get the total combinations S% ^. H P) d
The 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
