What is the last digit of 6 1 ! ?
Notation
:
!
denotes the
factorial
notation. For example,
8
!
=
1
×
2
×
3
×
⋯
×
8
.
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Very easy.
the last digit of every number n > 4 always is 0
∴ the last digit of 61! is 0 .
6 1 ! = 1 × 2 × 3 × 4 × 5 × ⋯ × 6 1
2 ∣ 6 1 ! , 5 ∣ 6 1 ! ⇒ 1 0 ∣ 6 1 !
The last digit is therfore 0
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5 ! will already give us 1 2 0 . Any positive integers we multiply by 1 2 0 will have a unit digit of 0
Therefore 6 1 ! will have a unit digit of 0