Answer
a. The probability of drawing one black, one red, and one white ball is 13/115.
b. The probability of drawing exactly two black balls is 27/92.
c. The probability of drawing no red balls is 1771/2300.
Solution
We are given a box with 25 balls. According to the problem, there are:
• 10 black balls,
• 2 red balls, and
• the rest are white.
Since the total is 25, the number of white balls is
25 – (10 + 2) = 13 white balls.
We draw three balls at random without replacement. The total number of possible draws is
Total outcomes = C(25, 3).
Recall that
C(n, k) = n!/(k!(n – k)!).
Thus,
C(25, 3) = 25×24×23 ÷ 6 = 2300.
Below are the solutions for each part:
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Part (a): One black, one red, and one white
Number of ways to choose:
• 1 black out of 10: C(10, 1)
• 1 red out of 2: C(2, 1)
• 1 white out of 13: C(13, 1)
Since these selections are independent, the number of favorable outcomes is
Favorable outcomes = C(10, 1) × C(2, 1) × C(13, 1) = 10 × 2 × 13 = 260.
Thus, the required probability is
P(a) = 260 / 2300.
You can simplify it by dividing numerator and denominator by 10:
P(a) = 26/230 = 13/115.
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Part (b): Exactly two are black
Here we want exactly 2 black balls and 1 ball that is not black (that is, either red or white).
Step 1. Choose 2 blacks out of 10:
C(10, 2).
Step 2. Choose 1 non-black from the remaining balls. The non-black balls total
2 (red) + 13 (white) = 15.
So, choose 1 out of 15: C(15, 1).
The number of favorable outcomes is
Favorable outcomes = C(10, 2) × C(15, 1).
Now, C(10, 2) = 10×9/2 = 45, so
Favorable outcomes = 45 × 15 = 675.
Thus, the probability is
P(b) = 675 / 2300.
You can simplify this fraction if desired. Dividing numerator and denominator by 5 gives:
675 ÷ 5 = 135 and 2300 ÷ 5 = 460,
so
P(b) = 135/460.
Dividing numerator and denominator by 5 again:
135 ÷ 5 = 27 and 460 ÷ 5 = 92,
thus
P(b) = 27/92.
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Part (c): None of them is red
For no red balls, all three balls must be chosen from the non-red balls. The number of non-red balls is
10 (black) + 13 (white) = 23.
So, the number of favorable outcomes is
Favorable outcomes = C(23, 3).
Thus, the probability is
P(c) = C(23, 3) / C(25, 3).
To compute C(23, 3):
C(23, 3) = 23×22×21 ÷ 6 = 1771.
So,
P(c) = 1771 / 2300.
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Summary of Answers:
a. P(one black, one red, one white) = [10×2×13] / C(25, 3) = 260/2300 = 13/115
b. P(exactly two black) = [C(10, 2) × C(15, 1)] / C(25, 3) = 675/2300 = 27/92
c. P(no red) = C(23, 3) / C(25, 3) = 1771/2300
These are the final answers for the problem.
Answered by UpStudy AI and reviewed by a Professional Tutor
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Simplify this solution