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Math Help - Please Help with probability?

  1. #1
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    Please Help with probability?

    These were the questions that i was stuck with when i was doing my probability homework, please help =)

    1) A die is rolled twice and the resulting numbers are added

    (a) Find the Probability that the sum is seven

    (b) What event(s) will give a probability of 1/9?


    2) A coin is tossed and a die is rolled.

    (a) Find the event(s) that will give a probability of 1/12

    (b) Find the event(s) that will give a probability of 1/6


    Please explain how to do this question, because i'm seriously stuck :'D

    Thanks for all the help!
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  2. #2
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    Quote Originally Posted by mathpro View Post
    These were the questions that i was stuck with when i was doing my probability homework, please help =)

    1) A die is rolled twice and the resulting numbers are added

    (a) Find the Probability that the sum is seven

    (b) What event(s) will give a probability of 1/9?


    2) A coin is tossed and a die is rolled.

    (a) Find the event(s) that will give a probability of 1/12

    (b) Find the event(s) that will give a probability of 1/6


    Please explain how to do this question, because i'm seriously stuck :'D

    Thanks for all the help!
    Q1 (a) Use the dice table here: Dice table

    (b) 1/9 = 4/36. Use the dice table to see what event(s) occurs 4 times ....


    Q2 Try constructing a coin-die table similar to the dice table above.

    (a) Use the coin-die table to see what events occur only once.

    (b) 1/6 = 2/12. Use the dice table to see what events occur 2 times ....

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  3. #3
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    Thanks for the help

    Thanks for the help, but i don't understand what you meant by teh 4/36 and to look on the dice table to check out what event(s) occur 4 times.

    But anyways thanks for the help, i appreciate it =)
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  4. #4
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    Probability

    Hello mathpro
    Quote Originally Posted by mathpro View Post
    These were the questions that i was stuck with when i was doing my probability homework, please help =)

    1) A die is rolled twice and the resulting numbers are added

    (a) Find the Probability that the sum is seven

    (b) What event(s) will give a probability of 1/9?


    2) A coin is tossed and a die is rolled.

    (a) Find the event(s) that will give a probability of 1/12

    (b) Find the event(s) that will give a probability of 1/6


    Please explain how to do this question, because i'm seriously stuck :'D

    Thanks for all the help!
    Since there are 6 ways in which the die can land each time there are 6 x 6 =36 ways in which it can land when rolled twice. You might find it helpful to plot these ways on an x-y (Cartesian) diagram. Suppose that x represents the score on the first throw, and y the score on the second throw. Then the point (2, 5), for example, represents a score of 2 on the first throw and 5 on the second.

    (a) Marks as dots all 36 possible points. They form a square pattern. Now put a little circle around any points giving a total score of 7 - the point (2, 5) will be one of them. These circled points form a simple pattern. So:

    • How many points are circled?
    • Given that the total number of points is 36, what is the probability that you get one of the circled points?

    (b) For an event to have a probability of 1/9, how many points will you need to circle? Can you see any patterns of points that will make this happen? Can you see what the answers are now? (There are two possible answers.)

    For question 2, try drawing another x-y diagram, except that this time x represents the score on the die (from 1 to 6) and y represents the flip of the coin (H or T). Mark as dots all 12 possible points. Then look for patterns that give probabilities of 1/2 and 1/6.

    I hope you can do it now.

    Grandad
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