Factorial triple fun part 1
Number Theory
Level
2
Solve this fun factorial problem:
The answer is 80.
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1 solution
Formula
n! = n(n-1)(n-2)(n-3)(n-4) ..
n!! = n(n-2)(n-4)(n-6) ..
n!!! = n(n-3)(n-6)(n-9) ..
Calculation
5!!! = 5(5-3) = 5(2) = 10
5!! = 5(5-2)(5-4) = 5(3)(1) = 15
5! = 5 * 4 * 3 * 2 * 1 = 120
Answer
5 ! ! 5 ! ! ! * 5!
1 5 1 0 * 120 = 80