If each of the students in a certain mathematics class is

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If each of the students in a certain mathematics class is [#permalink]

23 Aug 2010, 08:54

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If each of the students in a certain mathematics class is either a junior or a senior, how many students are in the class?
(1) If one student is to be chosen at random from the class to attend a conference,
the probability that the student chosen will be a senior is 4/7.
(2) There are 5 more seniors in the class than juniors.

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Re: Probability Concept -DS [#permalink]

23 Aug 2010, 09:24

udaymathapati wrote:

Let the # of seniors in the class be s and the # of juniors be j. Question: s+j=?

(1) If one student is to be chosen at random from the class to attend a conference, the probability that the student chosen will be a senior is 4/7 --> \frac{s}{s+j}=\frac{4}{7} --> 3s=4j: two variables, hence not sufficient to calculate s+j.

(2) There are 5 more seniors in the class than juniors --> s=j+5. Clearly not sufficient to calculate s+j.

(1)+(2) We have two different linear equations with 2 variables, hence we can find the values of both variables and calculate s+j. Sufficient.

Answer: C.
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Re: Probability Concept -DS [#permalink] 23 Aug 2010, 09:24

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If each of the students in a certain mathematics class is

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If each of the students in a certain mathematics class is

If each of the students in a certain mathematics class is

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