Step by step
The question
Question: work out 4 factorial.
4! =
1 Write it out
4 factorial means 4 times every whole number below it, down to 1.
4! = 4 × 3 × 2 × 1
Factorial: multiply down to 1.
n! = n × (n − 1) × … × 1
Careful!
Factorial means times, not plus.
Careful: not 4 + 3 + 2 + 1 = 10 ✗
2 Multiply
4 times 3 is 12.
12 times 2 is 24.
Times 1 changes nothing.
4 × 3 = 12
12 × 2 = 24
So 4 factorial is 24.
4! = 24
3 Check
Let's check the other way round: 1 times 2 is 2, then 6, then 24.
The same.
So the answer is right!
1 × 2 × 3 × 4: 2, 6, 24 ✓
Let's look back.
First: write it out.
Then: multiply.
Last: check.
Answer
4! = 24