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What is the units digit of 18! + 4!?

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What is the units digit of 18! + 4!?  [#permalink]

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New post 19 Apr 2016, 02:05
4
00:00
A
B
C
D
E

Difficulty:

  15% (low)

Question Stats:

79% (00:48) correct 21% (00:53) wrong based on 155 sessions

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What is the units digit of 18! + 4!?

A. 0
B. 1
C. 2
D. 3
E. 4
Spoiler: OA

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Re: What is the units digit of 18! + 4!?  [#permalink]

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New post 19 Apr 2016, 04:08
1
5
Bunuel wrote:
What is the units digit of 18! + 4!?

A. 0
B. 1
C. 2
D. 3
E. 4



Hi

anything above 4! such as 5!, 6! etc are always multiple of 10, so their units digit is 0..
So units digit of 18! + 4! will depend on 4! = 4*3*2=24
ans $
E
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Re: What is the units digit of 18! + 4!?  [#permalink]

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New post 19 Apr 2016, 07:59
1
Bunuel wrote:
What is the units digit of 18! + 4!?

A. 0
B. 1
C. 2
D. 3
E. 4


Check if there are trailing zeroes

4! /5 = Not divisible , hence there must be a numeric value of the units digit which is non zero

Calculate it 4! = 4*3*2*1 =>24

18! /5 is divisible m so it will have trailing zeroes

18! = Has units digit as 0

4! = Has units digit 4

So, Units digit of 18! + 4! will be 4
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Re: What is the units digit of 18! + 4!?  [#permalink]

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New post 19 Apr 2016, 09:17
18!
8 * 7 * 6 * 5 and it already ends there as units digits 5 and 6 will render 0

4 times 3 times 1 gives 4 as a units digit, 0 and 4 give 4
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Re: What is the units digit of 18! + 4!?  [#permalink]

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New post 21 Apr 2016, 10:30
any factorial greater than 4 must end in zero
so UD => 0+4 => 4
smash E
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Re: What is the units digit of 18! + 4!?  [#permalink]

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New post 21 Apr 2016, 16:09
1
2
The trick is to remember that any number above 4! such as 5!, 6! etc are always multiple of 10 (since they will have at least a 5 in the calculation), so their units digit is 0.

So units digit of 18! + 4! will depend on 4! which is
4*3*2=24
Correct Option : E
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Re: What is the units digit of 18! + 4!?  [#permalink]

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New post 15 Jul 2017, 04:38
1! = 1
2! = 2
3! = 6
4! = 24
5! = 120
6! = 720
7! = 5040

We can see that the any number's factorial, if that number is greater than 4 will have a units digit of 0.

Coming back to our question,
We have been asked to calculate the units digit of 18! + 4!,
which in essentially the units digit of 4! : 4(Option E)
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Re: What is the units digit of 18! + 4!?  [#permalink]

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