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| For integers a and b, is the expression ab – b even? https://gmatclub.com/forum/for-integers-a-and-b-is-the-expression-ab-b-even-242106.html |
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| Author: | Bunuel [ 06 Jun 2017, 11:42 ] |
| Post subject: | For integers a and b, is the expression ab – b even? |
For integers a and b, is the expression ab – b even? (1) a is odd (2) b is odd |
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| Author: | BrentGMATPrepNow [ 06 Jun 2017, 11:55 ] |
| Post subject: | Re: For integers a and b, is the expression ab – b even? |
Bunuel wrote: For integers a and b, is the expression ab – b even? (1) a is odd (2) b is odd Target question: Is the expression ab – b even? HINT: notice that ab – b = b(a - 1) Statement 1: a is odd What does does this tell us about the expression ab – b? Well, ab – b = b(a - 1) = b(ODD - 1) = b(EVEN) [since an odd integer minus 1 gives us a EVEN integer] = EVEN Since we can answer the target question with certainty, statement 1 is SUFFICIENT Statement 2: b is odd There are several values of a and b that satisfy statement 2. Here are two: Case a: a = 3 and b = 1. In this case ab – b = (3)(1) - 1 = 2. So, ab – b is EVEN Case b: a = 2 and b = 1. In this case ab – b = (2)(1) - 1 = 1. So, ab – b is ODD Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT Answer: Cheers, Brent |
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| Author: | Gnpth [ 25 Jul 2017, 17:49 ] |
| Post subject: | Re: For integers a and b, is the expression ab – b even? |
ab-b can be converted into b(a-1), We have to find either b or a-1 to be even. st-1 says a is odd. then a-1 is even. So the term b(a-1) will be even. sufficient. st-2 says b is odd. No info about a. so not sufficient. Answer is A. |
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| Author: | ocelot22 [ 16 Jan 2019, 13:20 ] |
| Post subject: | Re: For integers a and b, is the expression ab – b even? |
Bunuel wrote: For integers a and b, is the expression ab – b even? (1) a is odd (2) b is odd b(a-1) even? (1) a odd, then a-1 is even, then we have even *b = even sufficient (2) b odd. Let be =1 1(a-1) even? let a=1. Then ab-b = 1(0) = 0 Yes even. Let a=2 then ab-b 1(2-1) =1 No. Odd. NS Answer is A |
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| Author: | bumpbot [ 20 Dec 2022, 08:08 ] |
| Post subject: | Re: For integers a and b, is the expression ab b even? |
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