If a fair die is rolled 3 times, what is the probability that (a) a 5 will result 2 times out of the 3 rolls? (b) an odd number will result 2 times? (c) a number divisible by 3 will occur 3 times?
Addition Rule of Probability
It simply refers to the likelihood of an event taking place whenever the occurrence of an event is uncertain. The probability of a single event can be calculated by dividing the number of successful trials of that event by the total number of trials.
Expected Value
When a large number of trials are performed for any random variable ‘X’, the predicted result is most likely the mean of all the outcomes for the random variable and it is known as expected value also known as expectation. The expected value, also known as the expectation, is denoted by: E(X).
Probability Distributions
Understanding probability is necessary to know the probability distributions. In statistics, probability is how the uncertainty of an event is measured. This event can be anything. The most common examples include tossing a coin, rolling a die, or choosing a card. Each of these events has multiple possibilities. Every such possibility is measured with the help of probability. To be more precise, the probability is used for calculating the occurrence of events that may or may not happen. Probability does not give sure results. Unless the probability of any event is 1, the different outcomes may or may not happen in real life, regardless of how less or how more their probability is.
Basic Probability
The simple definition of probability it is a chance of the occurrence of an event. It is defined in numerical form and the probability value is between 0 to 1. The probability value 0 indicates that there is no chance of that event occurring and the probability value 1 indicates that the event will occur. Sum of the probability value must be 1. The probability value is never a negative number. If it happens, then recheck the calculation.
If a fair die is rolled 3 times, what is the probability that
(a) a 5 will result 2 times out of the 3 rolls?
(b) an odd number will result 2 times?
(c) a number divisible by 3 will occur 3 times?
(a)
A fair die is rolled 3 times.
Formula used:
The compliment of a probability p is,
q=1−p
Where, p is a probability of success, q is a probability of not success.
The binomial distribution probability of x success in n trials is,
P(X=x)=nCxpxqn-x
Where, p is a probability of success, q is a probability of not success, n is the number of independent trials and r is desired success.
Calculation:
Consider a fair die rolled 3 times,
Now, when a fair die is rolled one time the possible outcomes are, 1, 2, 3, 4, 5, and 6
The number of times 5 comes when a fair die is rolled is 1.
The probability for the outcome of 5 when a fair die is rolled, p=1/6
Use the formula for the compliment of probability p, q=1−p
Substitute 1/6 for p.
q=1−1/6=5/6
Use the formula of binomial distribution probability,
P(X=x)=nCxpxqn-x
Substitute 1/6 for p, 5/6 for q, 3 for n and 2 for x.
Pr(2 times 5)=3C2(1/6)2(5/6)3-2=3×1/36×5/6=5/72
Hence, the probability that a 5 will result 2 times out of 3 rolled is 5/72.
(b)
Now, when a fair die is rolled one time the possible outcomes are, 1, 2, 3, 4, 5, and 6
There are 3 odd number comes when a fair is rolled.
The probability for the result of an odd number when a fair die is rolled, p=3/6=1/2
Use the formula for the compliment of probability p, q=1−p
Substitute 1/2 for p.
q=1−(1/2)=1/2
Use the formula of binomial distribution probability,
P(X=x)=nCxpxqn-x
Substitute 1/2 for p, 1/2 for q, 3 for n and 2 for x.
Pr(2 times an odd number)= 3C2(1/2)2(1/2)3-2=3×(1/8)=3/8
Hence, the probability that an odd number will result 2 times if a fair die is rolled 3 times 3/8.
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