There are 5 balls, 2 marked "Yes" and 3 unmarked. Five people draw the balls one by one without replacement. The question asks if the probability that each person draws a "Yes" ball is the same.

Probability and StatisticsProbabilityConditional ProbabilityCombinatorics
2025/4/16

1. Problem Description

There are 5 balls, 2 marked "Yes" and 3 unmarked. Five people draw the balls one by one without replacement. The question asks if the probability that each person draws a "Yes" ball is the same.

2. Solution Steps

Let P(i)P(i) be the probability that the ii-th person draws a "Yes" ball.
For the first person, the probability of drawing a "Yes" ball is:
P(1)=Number of "Yes" ballsTotal number of balls=25P(1) = \frac{\text{Number of "Yes" balls}}{\text{Total number of balls}} = \frac{2}{5}
For the second person, we consider two cases:
Case 1: The first person drew a "Yes" ball. Then there is 1 "Yes" ball and 3 unmarked balls remaining, for a total of 4 balls. The probability of the second person drawing a "Yes" ball is 14\frac{1}{4}. The probability of this case happening is 25\frac{2}{5}.
Case 2: The first person drew an unmarked ball. Then there are 2 "Yes" balls and 2 unmarked balls remaining, for a total of 4 balls. The probability of the second person drawing a "Yes" ball is 24=12\frac{2}{4} = \frac{1}{2}. The probability of this case happening is 35\frac{3}{5}.
Thus, the probability of the second person drawing a "Yes" ball is:
P(2)=P(1st person drew "Yes")P(2nd person draws "Yes"1st person drew "Yes")+P(1st person drew unmarked)P(2nd person draws "Yes"1st person drew unmarked)P(2) = P(\text{1st person drew "Yes"}) \cdot P(\text{2nd person draws "Yes"} | \text{1st person drew "Yes"}) + P(\text{1st person drew unmarked}) \cdot P(\text{2nd person draws "Yes"} | \text{1st person drew unmarked})
P(2)=2514+3524=220+620=820=25P(2) = \frac{2}{5} \cdot \frac{1}{4} + \frac{3}{5} \cdot \frac{2}{4} = \frac{2}{20} + \frac{6}{20} = \frac{8}{20} = \frac{2}{5}
Now, let's check for the third person. We will consider two cases to see if the 3rd person draws a "Yes" ball:
Case 1: Two "Yes" were drawn in the first two draws. The probability of this is 2514=220\frac{2}{5} * \frac{1}{4} = \frac{2}{20}
The 3rd person's probability to draw "Yes" is 0 since there are no "Yes" balls left, 2200=0\frac{2}{20}*0 = 0
Case 2: One "Yes" and one unmarked were drawn in the first two draws. The probability of this is 2534+3524=620+620=1220\frac{2}{5} * \frac{3}{4} + \frac{3}{5} * \frac{2}{4} = \frac{6}{20} + \frac{6}{20} = \frac{12}{20}
The 3rd person's probability to draw "Yes" is 13\frac{1}{3}, so the probability of this case is 122013=1260\frac{12}{20} * \frac{1}{3} = \frac{12}{60}
Case 3: Two unmarked were drawn in the first two draws. The probability of this is 3524=620\frac{3}{5} * \frac{2}{4} = \frac{6}{20}
The 3rd person's probability to draw "Yes" is 23\frac{2}{3}, so the probability of this case is 62023=1260\frac{6}{20} * \frac{2}{3} = \frac{12}{60}
Adding the probabilities, we get 1260+1260=2460=25\frac{12}{60} + \frac{12}{60} = \frac{24}{60} = \frac{2}{5}
In general, the probability of drawing a "Yes" ball is the same for each person, which is 25\frac{2}{5}.

3. Final Answer

Yes, the probability that each person draws a "Yes" ball is the same.

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