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positive two digit number

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positive two digit number

by j_shreyans » Sat Mar 07, 2015 9:57 pm
If xy represents a positive two-digit number, where x and y are single digit integers, which of the following CANNOT be true?

A)x + y = 9
B)(x)(y) = 9
C)x - y = 9
D)y - x = 9
E)x/y = 9


I solved this question with correct answer.

But one thing i still want to know is that in option B

(x)(y)=9

we can solve like.

(3)(3)=9
(1)(9)=9
(9)(1)=9

i mean i can choose any one to solve.

Please advise.

Thanks ,

Shreyans
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by MartyMurray » Sat Mar 07, 2015 10:28 pm
Yes, you can choose any of them.

The only question here is that of whether it is possible for an answer choice to be true. B can be true in three different ways. A can also be true in multiple ways.

That's fine and doesn't make any difference. They can be true, and that's sufficient to answer the question, and in answering the question, as soon as you find one case that works, there's no need to take it any further.
Last edited by MartyMurray on Sat Mar 07, 2015 10:31 pm, edited 1 time in total.
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by [email protected] » Sat Mar 07, 2015 10:29 pm
Hi j_shreyans,

Your approach is correct. When a prompt uses the phrase "which of the following CANNOT be true?" what it's really asking is "which of the following can NEVER be true no matter how many how long you think about it and no matter how many examples you try to come up with?"

For Answer B, you came up with 3 different examples that all prove that Answer B CAN be true. Thus, you can eliminate this answer.

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by prachi18oct » Sun Mar 08, 2015 7:08 pm
Is the OA (D) ?
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by MartyMurray » Mon Mar 09, 2015 1:47 am
The OA is D.
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by prachi18oct » Mon Mar 09, 2015 4:21 am
So many duplicate posts by me. Probably some issue with posting as I could not see .
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by [email protected] » Mon Mar 09, 2015 10:07 am
Hi prachi18oct,

The correct answer is D

The reason why is because we're told that XY represents a two-digit number (e.g. 28, 43, 91, etc.) - X and Y are each DIGITS. As an individual digit, each can represent the numbers 0 through 9, inclusive. HOWEVER, as a two-digit number, the first digit CANNOT be 0 (e.g.. 02, 05, 08), since those examples are considered one-digit numbers. So, if the "X digit" has to be at least 1....then the Y-X can NEVER be 9.

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