Q. If a fair die is rolled 5 times, what is the probability, rounded to the nearest thousandth, of getting at most 1 four?Answer:
Determine Probability of Rolling: Determine the probability of rolling a four on a single die roll.A fair die has 6 sides, so the probability of rolling any specific number, including a four, is 61. Conversely, the probability of not rolling a four is 65.
Calculate Probability of One Four: Calculate the probability of rolling exactly one four in five rolls.This can happen in several different ways: the four can appear on the first, second, third, fourth, or fifth roll. We will use the binomial probability formula, which is P(X=k)=(kn)⋅(pk)⋅((1−p)(n−k)), where n is the number of trials, k is the number of successful outcomes we want, and p is the probability of success on a single trial.For exactly one four, k=1, n=5, and p=61. So we calculate:P(X=1)=(15)⋅(61)1⋅(65)5−1P(X=1)=5⋅(61)⋅(65)4
Calculate Probability of No Fours: Calculate the probability of rolling no fours in five rolls.For this scenario, k=0, n=5, and p=61. We use the binomial probability formula again:P(X=0)=(05)×(61)0×(65)5−0P(X=0)=1×1×(65)5
Add Probabilities for At Most One Four: Add the probabilities of rolling exactly one four and no fours to get the total probability of rolling at most one four.P(at most one 4)=P(X=0)+P(X=1)P(at most one 4)=(65)5+5⋅(61)⋅(65)4
Perform Calculations: Perform the calculations.P(X=0)=(65)5=(65)5≈0.40188P(X=1)=5×(61)×(65)4≈0.40188P(at most one 4)=0.40188+0.40188≈0.80376
Recalculate Probability of One Four: Step 5 (Correction): Perform the correct calculations.P(X=0)=(65)5≈0.40188 (corrected value)P(X=1)=5×(61)×(65)4≈0.40188 (incorrect value, needs to be recalculated)P(X=1)=5×(61)×(65)4=5×(61)×(1296625)≈0.32143P(at most one 4)=P(X=0)+P(X=1)=0.40188+0.32143≈0.72331
Round Final Probability: Round the final probability to the nearest thousandth. P(at most one 4)≈0.723 (rounded to the nearest thousandth)
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