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GRE Prep Club Team Member
Joined: 20 Feb 2017
Posts: 2506
Given Kudos: 1055
GPA: 3.39
A perfect number is one whose sum of factors other than the
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28 Oct 2020, 01:00
28 Oct 2020, 01:00
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33% (01:25) wrong based on 6 sessions
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A perfect number is one whose sum of factors other than the number itself is equal to the number. Which of the following numbers is a perfect number?
(A) 12
(B) 18
(C) 20
(D) 21
(E) 28
(A) 12
(B) 18
(C) 20
(D) 21
(E) 28
Re: A perfect number is one whose sum of factors other than the
[#permalink]
28 Oct 2020, 03:37
28 Oct 2020, 03:37
1
from the options taking factors of each integer except itself
A. factors of 12 1,2,3,4,6
sum of factors =16
so 12 is not a perfect number
B.factors of 18 1,2,3,6,9
sum of factors =21
so 18 is not a perfect number
C.factors of 20 1,2,4,5,10
sum of factors =22
so 20 is not a perfect number
D.factors of 21 1,3,7
sum of factors =11
so 21 is not a perfect number
E.factors of 12 1,2,4,7,14
sum of factors =28
so 28 is a perfect number
option E is correct
A. factors of 12 1,2,3,4,6
sum of factors =16
so 12 is not a perfect number
B.factors of 18 1,2,3,6,9
sum of factors =21
so 18 is not a perfect number
C.factors of 20 1,2,4,5,10
sum of factors =22
so 20 is not a perfect number
D.factors of 21 1,3,7
sum of factors =11
so 21 is not a perfect number
E.factors of 12 1,2,4,7,14
sum of factors =28
so 28 is a perfect number
option E is correct
gmatclubot
Re: A perfect number is one whose sum of factors other than the [#permalink]
28 Oct 2020, 03:37
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