ds test4 #23

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dunkin77
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Topic: ds test4 #23
PostThu Apr 05, 2007 6:03 pm
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Hi,

The answer is C) but I am not too sure why A) is a necessary information - please explain... thanks!

If x and y are positive integers and x is a multiple of y, is y = 2?
(1) y ≠ 1
(2) x + 2 is a multiple of y.
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jayhawk2001
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PostThu Apr 05, 2007 10:05 pm
We are given x = my

1 - insufficient. Just knowing y != 1 does not help

2 - insufficient. We have x+2 = ny. Subtracting the 2 equations,
we get

x+2 - x = ny - my
or (n-m)y = 2

Since we are dealing with +ve integers here, we have 2 possibilities

n-m = 2, y = 1
n-m = 1, y = 2

Taking 1 and 2 together, we know that y!=1, so it boils down to
n-m = 1, y = 2

Hence C
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dunkin77
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PostThu Apr 05, 2007 10:43 pm
Ohh very clear - thank you!! Very Happy
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