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Problem solving OG #26

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Problem solving OG #26

by shrikantkamble » Thu Jul 10, 2008 8:57 am
If the quotient a/b is positive, which of the following must be true?

A) a > 0
B) b > 0
C) ab > 0
D) a-b > 0
E) a + b > 0

OG answer is C.

After solving the problem I thought option C and D are possible.
according to my understanding,
a-b > 0
a -b + b > +b ( adding b on both sides)
a > b
a/b > b/b (dividing by b )
a/b > 1
Which is the expected answer.

Can you please tell me why option D is not feasible ?
Thanks & Regards,
Shrikant
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by gxliu » Thu Jul 10, 2008 8:58 am
question is asking MUST be true. Not if its feasbile. D is feasbile, but its not necessarily true. Only C MUST be true.
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by target790 » Thu Jul 10, 2008 9:30 am
D is not feasible if both a and b are negative .
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by fajoni » Fri Jul 11, 2008 12:14 pm
Picking numbers works well in illustrating why D does not absolutely have to be true.

If a/b is positive, we know that both a and b have the same sign. So what if A=-4 and B=-2...

-4/-2 = 2

-4 - (-2) =-2, thus, A - B does not have to be positive.

Good luck with the studying!
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