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Thread: Probability - Clock

  1. #1
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    Probability - Clock

    (a) Danielle has a battery-driven clock on her mantelpiece. What is the probability that the battery will run out when the clock is showing a time between two o'clock and quarter to three?

    (b) State whether you agree or disagree with each of the following statements. Give reasons for your answer.

    (i) Silver knight is one of twenty horses entered for the Grand National. The probability of Silver Knight winning is 1/20.

    (ii) There are four candidates at an election. The probability of each candidate winning the election is 1/4.

    (iii) The probability that the sun will shine in London on July 15th is 1/2.

    ---------------------------------------------------------------------------------------

    My attempt for (a): between 2 and quarter to three, there are 45 minutes, which means 3/4 of 1 hour (full circle). The probability is 3/4


    for (b):

    (i) Disagree (each horse has different speed and strength)

    (ii) Disagree (candidates are not selected randomly, so each one has different chances of winning)

    (iii) Agree (Everyday, including 15th of July, the Sun will either shine or not)
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  2. #2
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    Re: Probability - Clock

    For (a) the hour hand needs to be in a certain spot as well. Not just the minute hand. The clock distinctly represents every time in a 12 hour period with equal probability of any specific time. So, the probability is $\dfrac{3}{4\cdot 12} $
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  3. #3
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    Re: Probability - Clock

    Quote Originally Posted by joshuaa View Post
    (a) Danielle has a battery-driven clock on her mantelpiece. What is the probability that the battery will run out when the clock is showing a time between two o'clock and quarter to three?

    (b) State whether you agree or disagree with each of the following statements. Give reasons for your answer.

    (i) Silver knight is one of twenty horses entered for the Grand National. The probability of Silver Knight winning is 1/20.

    (ii) There are four candidates at an election. The probability of each candidate winning the election is 1/4.

    (iii) The probability that the sun will shine in London on July 15th is 1/2.

    ---------------------------------------------------------------------------------------

    (iii) Agree (Everyday, including 15th of July, the Sun will either shine or not)
    Weather is not random. The earth rotates 100% of the time. Clouds are covering the sun with a pattern of frequency difficult to calculate.
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  4. #4
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    Re: Probability - Clock

    Each of (i), (ii), and (iii) assume every outcome is "equally likely" which is seldom true.
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  5. #5
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    Re: Probability - Clock

    thanks.
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