HEREDITY
BASICS OF PROBABILITY
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Sarah rolls a standard die 120 times. How many times can she expect to roll a number larger than 4?
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120
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60
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40
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20
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Explanation:
Detailed explanation-1: -As given in another answer, the expected value is 20.
Detailed explanation-2: -For 12 rolls, two of them will be a 4. 10x12 = 120 so we expect 2x10 = 20 fours. Hence for 120 rolls, the expected number of 4s is 20.
Detailed explanation-3: -Rolling dice is an independent event, it is not dependent on how many times it’s been rolled. Probability of getting 1 two times in a row = probability of getting 1 first time×probability of getting 1 second time. Probability of getting 1 two times in a row = (1/6) × (1/6) = 1/36.
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