A pair of fair dice is thrown independently 3 times. The probability of getting a score of exactly 9 twice is
Explanation
1. Probability of a Single Event (Score of 9)
When two fair dice are thrown, the total number of outcomes is:
The pairs that result in a sum of 9 are:
Number of favorable outcomes, n(E)=4.
The probability of getting a score of 9 in one throw (p):
The probability of not getting a score of 9 (q):
2. Binomial Distribution Formula
For n independent trials, the probability of getting exactly r successes is:
Here:
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Total trials, n=3
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Successes required, r=2
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p=91
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q=98
3. Calculation
Substitute the values into the formula:
P(X=2)=(23)(91)2(98)3−2
Since (23)=3:
Simplify the fraction by dividing numerator and denominator by 3:
Final Answer:
The probability of getting a score of exactly 9 twice is: