Permutations & Combinations

Front

What is a permutation?

Back

A permutation is an arrangement of objects in a specific order. The order matters.

Front

What is a combination?

Back

A combination is a selection of objects where the order does not matter.

Front

When would you use a permutation instead of a combination?

Back

Use a permutation when the arrangement or order of the selected items is important.

Front

When would you use a combination instead of a permutation?

Back

Use a combination when the arrangement or order of the selected items is not important.

Front

How many ways can you arrange 3 books from a shelf of 5 books?

Back

60 ways (5P3 = 5!/(5-3)! = 60).

Front

How many ways can you choose 2 fruits from a selection of 4 fruits?

Back

6 ways (4C2 = 4!/(2!(4-2)!) = 6).

Front

What is the formula for permutations of n items taken r at a time?

Back

The formula is nPr = n! / (n - r)!.

Front

What is the formula for combinations of n items taken r at a time?

Back

The formula is nCr = n! / (r!(n - r)!).

Front

If you have 6 different questions and need to choose 3, how many combinations can you make?

Back

20 combinations (6C3 = 6!/(3!(6-3)!) = 20).

Front

If you have 8 horses in a race, how many ways can you pick the first 3 places?

Back

336 ways (8P3 = 8!/(8-3)! = 336).