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There are only green pens and red pens in a box. There are 3 more red pens than green pens in the box. Sheila is going to take at random two pens from the box. The probability that Sheila will take two pens of the same color is ( frac(17)(35) ). Work out two different numbers of green pens that could be in the box.

A) 5
B) 7
C) 10
D) 14

User Gilda
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1 Answer

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Final answer:

In this high school mathematics problem, we need to find two different numbers of green pens in a box, given the probability of selecting two pens of the same color as \(\frac{17}{35}\). By setting up an equation using combinations and comparing all the options, we find that only Option A (5 green pens) satisfies the given probability condition.

Step-by-step explanation:

The question involves determining the number of green pens in a box, given that the probability of selecting two pens of the same color is \(\frac{17}{35}\). We are told there are 3 more red pens than green pens. Let's denote the number of green pens as G and red pens as G + 3. The probability of picking two pens of the same color is the sum of the probability of picking two green pens plus the probability of picking two red pens. This can be calculated using combinations.

The probability of picking two green pens is given by \(P(GG) = \frac{{C(G, 2)}}{{C(G + G + 3 , 2)}}\) and the probability of picking two red pens is \(P(RR) = \frac{{C(G + 3, 2)}}{{C(G + G + 3, 2)}}\). The total probability is then \(P(GG) + P(RR) = \frac{17}{35}\).

To solve for G, we set up the equation: \(\frac{{C(G, 2) + C(G + 3, 2)}}{{C(2G + 3, 2)}} = \frac{17}{35}\). Solving for G in this equation will yield the number of green pens. Evaluating the given options:

  • Option A (5 green pens): The total number of pens would be \(5+5+3=13\). The probability of picking two pens of the same color is \(\frac{{C(5, 2) + C(8, 2)}}{{C(13, 2)}} = \frac{17}{35}\), which satisfies the probability condition.
  • Option B (7 green pens): The total number of pens would be \(7+7+3=17\). The probability of picking two pens of the same color is \(\frac{{C(7, 2) + C(10, 2)}}{{C(17, 2)}}\), which does not satisfy the probability condition.
  • Option C (10 green pens): The total number of pens would be \(10+10+3=23\). The probability of picking two pens of the same color is \(\frac{{C(10, 2) + C(13, 2)}}{{C(23, 2)}}\), which does not satisfy the probability condition.
  • Option D (14 green pens): The total number of pens would be \(14+14+3=31\). The probability of picking two pens of the same color is \(\frac{{C(14, 2) + C(17, 2)}}{{C(31, 2)}}\), which does not satisfy the probability condition.

Therefore, the possible number of green pens that satisfy the given probability are 5 green pens from Option A.

User Vitjbr
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