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Is xy<15? 1) x<3 2) y<5

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Is xy<15? 1) x<3 2) y<5 [#permalink]

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New post 03 Oct 2017, 01:37
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A
B
C
D
E

Difficulty:

  25% (medium)

Question Stats:

74% (00:23) correct 26% (00:22) wrong based on 38 sessions

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[GMAT math practice question]

Is xy<15?

1) x<3
2) y<5
[Reveal] Spoiler: OA

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Re: Is xy<15? 1) x<3 2) y<5 [#permalink]

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New post 03 Oct 2017, 02:12
MathRevolution wrote:
[GMAT math practice question]

Is xy<15?

1) x<3
2) y<5


Statement 1: no value of \(y\) is given. Insufficient

Statement 2: no value of \(x\) is given. Insufficient

Combining 1 & 2, if \(x=2\), \(y=4\), then \(xy=8<15\) but if \(x=-10\), \(y=-2\), then \(xy=20>15\). Hence Insufficient

Option E

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Re: Is xy<15? 1) x<3 2) y<5 [#permalink]

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New post 05 Oct 2017, 03:12
=>

Forget conventional ways of solving math questions. In DS, VA (Variable Approach) method is the easiest and quickest way to find the answer without actually solving the problem. Remember that equal number of variables and independent equations ensures a solution.

There are 2 variables and 0 equation. Therefore, C is most likely to be the answer.

Conditin 1) & 2)
x = 1, y = 2 ➔ xy = 2 < 15 : Yes
x = -4, y = -4 ➔ xy = 16 > 16 : No

Therefore, unlike our expectation, E is the answer.

Normally for cases where we need 2 more equations, such as original conditions with 2 variables, or 3 variables and 1 equation, or 4 variables and 2 equations, we have 1 equation each in both con 1) and con 2). Therefore, C has a high chance of being the answer, which is why we attempt to solve the question using con 1) and con 2) together. Here, there is 70% chance that C is the answer, while E has 25% chance. These two are the key questions. In case of common mistake type 3,4, the answer may be from A, B or D but there is only 5% chance. Since C is most likely to be the answer according to DS definition, we solve the question assuming C would be our answer hence using con 1) and con 2) together. (It saves us time). Obviously, there may be cases where the answer is A, B, D or E.

Ans: E
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Re: Is xy<15? 1) x<3 2) y<5   [#permalink] 05 Oct 2017, 03:12
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