Curriculum › Math ›Grade 4

Grade 4 Math · Level 5, Patterns, Data Literacy, Counting & Probability

Factorials & Arrangements

How the lesson starts: Factorials & Arrangements

1. Photo day at the farm

   Say cheese! Farmer Flo is taking a photo of three friends. Meet Moo the cow, Oink the pig and Baa the sheep. They want to stand in a different order every time. How many different orders can they make?

2. List every order

   Let's list them neatly. Put the cow first: two orders. Put the pig first: two orders. Put the sheep first: two more. That's 6 different photos!

3. The factorial sign

   Here's why. The first spot has 3 choices. Then 2 are left, then 1. So 3 × 2 × 1 = 6. Mathematicians write 3! for that, and call it three factorial. Start at the number and multiply all the way down to 1.