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07 May 2017, 10:20
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C
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Difficulty:
75%
(hard)
Question Stats:
34% (01:13) correct
66%
(01:07)
wrong
based on 156
sessions
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If x and y are positive integers, what is the greatest common divisor of x and y?
(1) x and y are both prime Numbers
(2) x + y is odd.
(1) x and y are both prime Numbers
(2) x + y is odd.
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07 May 2017, 10:32
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ans is A
as prime numbers, greatest common divisor must be 1.
2 doesn't serve any purpose.
Sent from my BLN-L22 using GMAT Club Forum mobile app
as prime numbers, greatest common divisor must be 1.
2 doesn't serve any purpose.
Sent from my BLN-L22 using GMAT Club Forum mobile app
07 May 2017, 10:34
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If x and y are positive integers, what is the greatest common divisor of x and y?
(1) x and y are both prime numbers. If x and y are different primes, say 2 and 3, then the the greatest common divisor of x and y will be 1 but if x and y are the same prime, say 2 and 2, then the the greatest common divisor of x and y will be that prime. Not sufficient.
Note here that unless it is explicitly stated otherwise, different variables CAN represent the same number.
(2) x + y is odd. This implies that one is odd and another is even. Clearly not sufficient. For example, x = 1 and y = 2, then GCF = 1 but x = 3 and y = 6, then GCF = 3.
(1)+(2) From (2) it follows that x and y cannot be the same prime, because in this case x + y would be even. Thus x and y are different primes, which implies that the greatest common divisor of x and y is 1. Sufficient.
Answer: C.
Hope it's clear.
(1) x and y are both prime numbers. If x and y are different primes, say 2 and 3, then the the greatest common divisor of x and y will be 1 but if x and y are the same prime, say 2 and 2, then the the greatest common divisor of x and y will be that prime. Not sufficient.
Note here that unless it is explicitly stated otherwise, different variables CAN represent the same number.
(2) x + y is odd. This implies that one is odd and another is even. Clearly not sufficient. For example, x = 1 and y = 2, then GCF = 1 but x = 3 and y = 6, then GCF = 3.
(1)+(2) From (2) it follows that x and y cannot be the same prime, because in this case x + y would be even. Thus x and y are different primes, which implies that the greatest common divisor of x and y is 1. Sufficient.
Answer: C.
Hope it's clear.
