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Is ab(b - 4) a positive integer?
(1) Both a and b are positive integers
(2) b - 1 = 63/(b + 1)
(1) Both a and b are positive integers
(2) b - 1 = 63/(b + 1)
Archived Topic
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This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
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14 Nov 2014, 11:55
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statement 1: not sufficient
If a and b are each 1, then the equation would be negative. If a and b are each 5, then the equation would be positive.
statement 2: not sufficient
no info on A
down to answers C and E
Using both statements together - statement 2 can help us find b
1. multiply both sides by (b+1) to get (b-1)(b+1)=63
2. factor to get (b^2 - 1 ) = 63
3. subtract 63 from both sides to get b^2 - 64 = 0
4. unfactor to get (b+8)(b-8) = 0. b is either -8 or 8
Statement 1 tells us a and b are positive so with statement 2 we know that b=8. Now we can plug into the original equation ab(b-4) to get 8a(8-4) or 8 * a * 4. Since a is positive as well as the other numbers we are multiplying, we know that the equation must equal a positive number.
Answer C!!
If a and b are each 1, then the equation would be negative. If a and b are each 5, then the equation would be positive.
statement 2: not sufficient
no info on A
down to answers C and E
Using both statements together - statement 2 can help us find b
1. multiply both sides by (b+1) to get (b-1)(b+1)=63
2. factor to get (b^2 - 1 ) = 63
3. subtract 63 from both sides to get b^2 - 64 = 0
4. unfactor to get (b+8)(b-8) = 0. b is either -8 or 8
Statement 1 tells us a and b are positive so with statement 2 we know that b=8. Now we can plug into the original equation ab(b-4) to get 8a(8-4) or 8 * a * 4. Since a is positive as well as the other numbers we are multiplying, we know that the equation must equal a positive number.
Answer C!!
Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Data Sufficiency (DS) Forum
Still interested in this question? Check out the "Best Topics" block above for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!
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