What is
Think | Write |
---|---|
You need the formula for number of combinations. Substitute 13 for n and 4 for r. |
|
Write out the top factorial—but only so far. Remove common factors. |
Image Long Description |
When determining whether to use a permutation or combination, you must decide whether order is important.
For each situation, determine whether you should use a permutation or combination. What is the answer to each question?
How will you solve?
If order is important, use the formula
A chemistry teacher divides his class into eight groups. Each group submits one drawing of the molecular structure of water. He will select four of the drawings to display. In how many different ways can he select the drawings?
There is no reason why order is important. Use a combination.
There are 70 ways to select the drawings.
You will draw winners from a total of 25 tickets in a raffle. The first ticket wins $100. The second ticket wins $50. The third ticket wins $10. In how many different ways can you draw the three winning tickets?
Values of the tickets depend on the order in which you draw them. Order is important. Use a permutation.
There are 13,800 ways you can draw the winning tickets.