If positive integer x is a multiple of 6 and positive integer y is a multiple of 14, is xy a multiple of 105?
(1) x is a multiple of 9.
(2) y is a multiple of 25.
Number prop
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- Morgoth
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beater wrote:If positive integer x is a multiple of 6 and positive integer y is a multiple of 14, is xy a multiple of 105?
(1) x is a multiple of 9.
(2) y is a multiple of 25.
x = 2*3
y = 2*7
105 = 5*3*7
x*y = 2*3*2*7
Statement (1)
x = 3*3, we already know x = 2*3
x could be have 7 and 5 and cannot have 7 and 5. Insufficient.
Statement (2)
y= 5*5
for 105 we need 5*3*7. We already know, y=2*7, x = 2*3
x*y = 5*5*2*7*2*3
Sufficient.
Thus, B is the answer.
- Stuart@KaplanGMAT
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Morgoth wrote:beater wrote:If positive integer x is a multiple of 6 and positive integer y is a multiple of 14, is xy a multiple of 105?
(1) x is a multiple of 9.
(2) y is a multiple of 25.
x = 2*3
y = 2*7
105 = 5*3*7
x*y = 2*3*2*7
Great breakdown, but I'd go one step further at this point:
For xy to be a multiple of 105, we need at least one 3, 5 and 7 among the factors. We have a 3 and a 7, so the only missing factor is a 5.
(1) x is a multiple of 9
Doesn't say anything about our missing 5: insufficient.
(2) y is a multiple of 25
Yay! 25 = 5*5, so we have our missing factor: sufficient.
Stuart Kovinsky | Kaplan GMAT Faculty | Toronto
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