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Contests
National and Regional Contests
India Contests
India LIMIT
2019 LIMIT
2019 LIMIT Category B
Problem 2
units digit of factorial sum
units digit of factorial sum
Source: LIMIT 2019 CAS2 P7
April 28, 2021
factorial
number theory
Problem Statement
The digit in unit place of
1
!
+
2
!
+
…
+
99
!
1!+2!+\ldots+99!
1
!
+
2
!
+
…
+
99
!
is
<
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a
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(
A
)
<
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3
<span class='latex-bold'>(A)</span>~3
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(
A
)
<
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3
<
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(
B
)
<
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0
<span class='latex-bold'>(B)</span>~0
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(
B
)
<
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0
<
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>
(
C
)
<
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>
1
<span class='latex-bold'>(C)</span>~1
<
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(
C
)
<
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>
1
<
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>
(
D
)
<
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>
7
<span class='latex-bold'>(D)</span>~7
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(
D
)
<
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>
7
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