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Re: x gallon 40% alcohol solution is mixed with another y gallon10% alcoho [#permalink]
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What if y<x<1? The solution would not stand in that case.
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Re: x gallon 40% alcohol solution is mixed with another y gallon10% alcoho [#permalink]
This is a great question and the key to solving it is to quickly recognize that it's all about weighted averages.

x gallon 40% alcohol solution is mixed with another y gallon 10% alcohol solution to result is z gallon p% alcohol solution. Is p>25?

1) x2>y2
Sufficient.
What this tells us is that x > y. If X is greater than Y, then the resulting concentration of alcohol in the final solution is NECESSARILY greater than 25 b/c there is more of that particular solution. Note that the midpoint b/w 10 and 40 is 25.

2) z>p
Insufficient. Following the same logic as statement 1, we can see that this can go one of two ways. If we got a lot more of solution y, then clearly the concentration of alcohol will be biased towards 10%. Conversely, if we got more of x, then there will be a higher concentration of alcohol >25.
The fact that it can go both ways means insufficient.
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Re: x gallon 40% alcohol solution is mixed with another y gallon10% alcoho [#permalink]
What if x<y<1? no where it is mentioned that x is more than 1 gallon. Is the first statement still correct.
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Re: x gallon 40% alcohol solution is mixed with another y gallon10% alcoho [#permalink]
Expert Reply
 
salilbagai wrote:
\(x\) gallon 40% alcohol solution is mixed with another \(y\) gallon 10% alcohol solution to result is \(z\) gallon \(p\)% alcohol solution. Is \(p>25\)?

1) \(x^2>y^2\)
2) \(z > p\)


What if x<y<1? no where it is mentioned that x is more than 1 gallon. Is the first statement still correct.

­Since x and y must be positive numbers, then x^2 > y^2 implies that x > y > 0 (no 0 < x < y < 1 would satisfy x^2 > y^2). Hence, we used more 40% alcohol solution than 10% alcohol solution. If we had used an equal amount of these solutions, the final mixture would have a strength of exactly (40% + 10%)/2 = 25%. However, since we used more 40% alcohol solution than 10% alcohol solution, the final mixture would have a strength of more than 25%.

Hope it helps.
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Re: x gallon 40% alcohol solution is mixed with another y gallon10% alcoho [#permalink]
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