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Re: x percent of what number is equal to y?
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07 Sep 2016, 23:10
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let the number be z, hence question asking x percent of what number is equal to y is x/100(z) = y A) x=10y i.e. y=x/10 putting this value is the question equation => x/100(z) = x/10 i.e z=10 , sufficient
B) xy= 40 i.e. y=40/x => x/100(z) = 40/x => x^2(z) = 400 , can't be solved for z , not sufficient.
Re: x percent of what number is equal to y?
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09 Sep 2016, 06:38
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Top Contributor
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MathRevolution wrote:
x percent of what number is equal to y?
1) x = 10y 2) xy = 40
Target question:x percent of what number is equal to y? This is a good candidate for rephrasing the target question
x percent of what number is equal to y? Let k = the number we're trying to determine
We get: "If x percent of k is equal to y, what is the value of k? In other words, x/100 of k = y Or....(x/100)(k) = y To solve for k, multiply both sides by 100/x. We get: k = 100y/x
Let's REPHRASE the target question..... Target question:What is the value of 100y/x? So, all we need to do now is find the value of x/y
Statement 1: x = 10y Divide both sides by x to get: 1 = 10y/x Divide both sides by 10 to get: 1/10 = y/x PERFECT! If y/x = 1/10, then 100y/x = 100(1/10) = 10 Since we can answer the REPHRASED target question with certainty, statement 1 is SUFFICIENT
Statement 2: xy = 40 This is NOT enough information to find the value of 100y/x Consider these two conflicting cases: Case a: x = 2 and y = 20, in which case 100y/x = 100(20)/(2) = 1000 Case b: x = 20 and y = 2, in which case 100y/x = 100(2)/(20) = 10 Since we cannot answer the REPHRASED target question with certainty, statement 2 is NOT SUFFICIENT
Re: x percent of what number is equal to y?
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10 Sep 2016, 21:31
If we modify the original condition and the question, we get x(1/100)(some)=y. So we have to find x/y. In case of condition 1), we get x/y=10. The condition is sufficient and the correct answer is A.