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If 'a' and 'b' are positive integers, all of the following can be the

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If 'a' and 'b' are positive integers, all of the following can be the  [#permalink]

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New post 20 Jan 2020, 23:43
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If 'a' and 'b' are positive integers, all of the following can be the highest common divisor of 39a and 15b EXCEPT:

A. 5
B. 13
C. 39a
D. 15b
E. 15a
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If 'a' and 'b' are positive integers, all of the following can be the  [#permalink]

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New post 21 Jan 2020, 00:05
ann1111 wrote:
If 'a' and 'b' are positive integers, all of the following can be the highest common divisor of 39a and 15b EXCEPT:

A. 5
B. 13
C. 39a
D. 15b
E. 15a


A. 5 may be the GCD of 39a and 15b for a = 5 and b = 1
B. 13 may be the GCD of 39a and 15b for a = 1 and b = 13
C. 39a may be the GCD of 39a and 15b for b = 13a
D. 15b may be the GCD of 39a and 15b for a = 5b
E. 15a can NOT be the GCD of 39a and 15b because 39a is NOT divisible by 15a i.e. 39a/15a ≠ Integer
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Re: If 'a' and 'b' are positive integers, all of the following can be the  [#permalink]

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New post 21 Jan 2020, 03:39
ann1111 wrote:
If 'a' and 'b' are positive integers, all of the following can be the highest common divisor of 39a and 15b EXCEPT:

A. 5
B. 13
C. 39a
D. 15b
E. 15a


What is the source? The question doesn't make sense. 39a and 15b are both clearly divisible by 3, so the GCD of both will necessarily be divisible by 3. So neither of answers A or B can possibly be the GCD of the two numbers. Nor can answer E, so the question has three right answers.
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Re: If 'a' and 'b' are positive integers, all of the following can be the   [#permalink] 21 Jan 2020, 03:39
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