Q. If a fair die is rolled 5 times, what is the probability, rounded to the nearest thousandth, of getting at most 2 threes?Answer:
Understand the problem: Understand the problem.We need to calculate the probability of rolling at most 2 threes in 5 rolls of a fair die. This means we need to find the probability of rolling 0, 1, or 2 threes.
Calculate probabilities: Calculate the probability of rolling exactly 0, 1, or 2 threes.The probability of rolling a three on a single roll is 61, and the probability of not rolling a three is 65.
Calculate 0 threes: Calculate the probability of rolling exactly 0 threes.This is the same as rolling a non-three 5 times in a row, which is (65)5.
Calculate 1 three: Calculate the probability of rolling exactly 1 three.This can happen in 5 different ways (one for each roll being the three), and the probability for each way is (61)×(65)4. So, the total probability is 5×(61)×(65)4.
Calculate 2 threes: Calculate the probability of rolling exactly 2 threes.This can happen in several different ways. We can use the binomial coefficient to determine the number of ways to choose 2 rolls out of 5 to be threes. The binomial coefficient is "5 choose 2", which is 5!/(2!∗(5−2)!). This equals 10. The probability for each way is (1/6)2∗(5/6)3. So, the total probability is 10∗(1/6)2∗(5/6)3.
Add probabilities: Add the probabilities of rolling exactly 0, 1, or 2 threes to get the total probability.P(0 threes)+P(1 three)+P(2 threes)=(65)5+5×(61)×(65)4+10×(61)2×(65)3.
Calculate and add: Calculate the probabilities and add them together.P(0 threes)=(65)5=0.40188 approximately,P(1 three)=5×(61)×(65)4=0.40188 approximately,P(2 threes)=10×(61)2×(65)3=0.16075 approximately.Adding them together gives 0.40188+0.40188+0.16075=0.96451.
Round the result: Round the result to the nearest thousandth.The total probability rounded to the nearest thousandth is 0.965.