Answer:
P(A∩B) = 0
P(A) = 0.1667
P(B) = 0.8333
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Step-by-step explanation:
The events
- A = a 5 is observed on the first roll
- B = it takes at least two rolls for the first 5 to be observed
are mutually exclusive. There isn't any overlap. This is because event B involves "at least 2 rolls", meaning we cannot get 5 on the first roll. Either event A happens, or B does, but not both at the same time.
This allows us to say P(A∩B) = 0
In a venn diagram, the overlapped region between circles A and B would have probability 0 marked inside.
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P(A) = 1/6 since there is exactly one side labeled "5" out of 6 sides total. This converts to the approximate decimal form 1/6 = 0.1667 when rounding to four decimal places. The 6's go on forever, but of course we have to round at some point.
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We found that P(A) = 1/6. The complement to this is 1-(1/6) = 5/6, which is the probability of rolling anything but a "5". This fraction represents the scenario "at least 2 rolls are needed for the 1st '5' to show up" since we forced the first roll to be anything but 5.
Put another way, we have two options:
- Option 1: The first roll is "5". The probability is 1/6
- Option 2: The first roll is NOT "5" (so you'll need to do at least another roll to get "5"). The probability is 5/6.
The two probabilities 1/6 and 5/6 add to 6/6, aka 1, to represent 100% of all possible cases. This means P(A)+P(B) = 1 for this scenario.
The fraction 5/6 converts to the approximate decimal form of 5/6 = 0.8333; use a calculator or long division to determine this value.