Need help in solving the below DS problem

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Need help in solving the below DS problem

by sudeep88u » Sun Nov 16, 2014 10:07 pm
Hi All,

Below seen is a DS question that was thrown in during the GMAT PREP 1 Exam. Since this exam does not provide explanations for the correct /wrong answers, i request you to help me find an explanation to the below answer choice.


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Could you please tell me why is the answer choice C for the above question? I find that statement A alone is enough and hence answer should be A . I find this dubious.Please advice

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by [email protected] » Sun Nov 16, 2014 11:36 pm
Hi sudeep88u,

In this type of question, a "recipe" is just a set of cooking instructions - it does NOT tell you how many servings a person actually chose to make.

In this prompt, we're told that 4 servings requires 1.5 cups of pasta, but we DO NOT know how many servings Malik made (or chooses to make). We're asked how much pasta Malik will need the NEXT TIME he prepares the dish.

Fact 1 refers to "half" the servings he made the last time, but we don't know how many servings he made last time. Maybe he made 4 servings, maybe he made 8 or 12 or 16, etc. so Fact 1 is INSUFFICIENT. Fact 2 is also INSUFFICIENT. Combined though, we know how many servings Malik made "last time" and that he will make half as much as the next time.

Final Answer: C

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by sudeep88u » Mon Nov 17, 2014 12:05 am
Thank you so much for the quick response Rich!!

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by [email protected] » Mon Nov 17, 2014 8:13 am
Malik's recipe for 4 servings of a certain dish requires 1 1/2 cups of pasta. According to this recipe, what is the number of cups pasta that Malik will use the next time he prepares this dish?

1) The next time he prepare this dish, Malik will make half as many servings as he did the last time he prepared the dish

2) Malik used 6 cups of pasta the last time he prepared this dish
Target question: How many cups of pasta will Malik use the next time he prepares this dish?

Given: 4 servings of a certain dish requires 1 1/2 cups of pasta.
So, if we can determine the NUMBER OF DISH SERVINGS Malik prepares, we can determine how much past is required.

Statement 1: The next time he prepare this dish, Malik will make half as many servings as he did the last time he prepared the dish
We have no idea how many servings Malik made last time. So, we cannot determine the number of servings he'll make next time.
So, statement 1 is NOT SUFFICIENT

Statement 2: Malik used 6 cups of pasta the last time he prepared this dish
This information does not help us determine how much pasta he'll need NEXT TIME.
So, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
Statement 2: Malik used 6 cups of pasta the last time
Statement 1: Next time, Malik will make half as many servings as he did the last time. If we makes half as many servings, Malik will need half as much pasta as he needed last time.
So, Malik will need 3 cups of pasta next time
Since we can answer the target question with certainty, the combined statements are SUFFICIENT

Answer = C

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by Mathsbuddy » Wed Nov 19, 2014 8:22 am
Number of servings S = 1.5/4 C where C = number of cups of pasta
So C = 8/3 x S
Therefore to know C, we need to know S.

Statement 1 gives us a formula: S(next) = f x S(previous) where f is a given fraction
As S(previous) is undefined, so NOT SUFFICIENT to find S

Statement 2 gives us no information for C(next), so NOT SUFFICIENT either

Combined:C = 8/3 x S = 8/3 x f x S(previous) = 8/3 x f x [3/8 x C(previous)]
All variables are accounted for: SUFFICIENT