This module will make heavy use of the 'Law of Combining', which you probably learned in grade school, but without the fancy name. For example, in grade school you got a problem something like this:
Nancy Drew, girl detective, is heading out to Solve the Case. She has 3 blouses and 4 skirts in her closet (the housekeeper is behind on the laundry). How many different outfits can Nancy make?
Here is one way to visualize Nancy 's outfits:
Here is another way (called a tree diagram):
Either way, you have to agree that Nancy has 12 possible outfits (although her father, famous lawyer Carson Drew, will probably veto the tank-top/miniskirt combination).
You will probably also have noticed that 12 = 3 * 4, which is not a coincidence. There are 3 kinds of tops Nancy could put on, and for each of these, she could choose 4 skirts.
The Law of Combining says:
If you want to count the possible combinations of ONE PICK from set 1 and ONE PICK from set 2, you can just multiply the size of set 1 by the size of set 2.
Ntot = N1 * N2
After the Drews' housekeeper catches up with the laundry, Nancy has 17 blouses and 32 skirts. How many outfits can she make?
- I need a hint ... : remember to multiply the number in the first set by the number in the second set.
- ...another hint ... : the first set consists of 17 blouses...
I think I have the answer: 544.
No calculator? Just pull out your trusty slide rule.
No slide rule? Go to Google, type in the equation (i.e., "17*32=") and hit enter!
No browser? Get Firefox! Web designers everywhere will thank you. And you can tab to a new page to make your calculations on Google.
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