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    Leshan's Avatar
    Leshan Posts: 4, Reputation: 1
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    #1

    Jan 31, 2011, 09:21 AM
    Probability
    What is the probabilty of throwing a sum of 15 on three rolls of a fair die if the first roll is 4?
    ebaines's Avatar
    ebaines Posts: 12,131, Reputation: 1307
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    #2

    Jan 31, 2011, 09:26 AM

    If the first rol is a 4, that means that to win the sum of the next two rolls must be 11 (otherwise the sum af all three won't add to 15). Now, to get 11 on two rolls you must roll either a 5 followed by a 6, or a 6 followed by a 5 - there sre no other combinations of two rolls that will work. Can you figure the probability of either of those two sequences occurring?
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