Exercise · ZW-FACTORIAL-010 · ★★★ Advanced
How many trailing zeros does \(20!\) have? (Each trailing zero comes from a factor 10 = 2 · 5.)
Choose one option.
Show answer
- B. \(4\)
Explanation
The factors of 5 in \(20!\) come from 5, 10, 15 and 20: that is 4, and there are plenty of 2s. So there are 4 zeros (\(20!=2432902008176640000\)).
Review the concept: Factorial
The factorial of an integer \(n\ge 0\), written \(n!\), is the product of the positive integers less than or equal to \(n\); that of zero is one by convention.
\[n!=n(n-1)\cdots 2\cdot 1,\quad 0!=1\]
More practice problems: factorial
- ZW-FACTORIAL-001 Compute 5!.
- ZW-FACTORIAL-002 In how many ways can 6 different people line up in a row?
- ZW-FACTORIAL-003 Compute (6!)/(4!).
- ZW-FACTORIAL-004 Why is 0! defined as 1?
- ZW-FACTORIAL-005 For n≥ 0, which equals (n+1)!?
- ZW-FACTORIAL-006 Compute (8!)/(6! 2!).
- ZW-FACTORIAL-007 Simplify (n!)/((n-2)!) for n≥ 2.
- ZW-FACTORIAL-008 Words of 4 letters are formed from A, B, C, D (no repetition). How many start with A?