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Thread: Traffic light probability question.Need help!!

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    Traffic light probability question.Need help!!




    Hi,
    Need help to solve this probability question.

    At a certain traffic signal red for 30 seconds, yellow for 5 seconds, and green for 25 seconds. Find the probability that out of the next ten cars that arrive randomly at the light, exactly four will be stopped by a red light.
    a. 0.2
    b. 0.38
    c. 0.625
    d. 0.5

    Thanks in Advance!

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    Re: Traffic light probability question.Need help!!

    Quote Originally Posted by Shashank Prasad View Post
    Hi,
    Need help to solve this probability question.

    At a certain traffic signal red for 30 seconds, yellow for 5 seconds, and green for 25 seconds. Find the probability that out of the next ten cars that arrive randomly at the light, exactly four will be stopped by a red light.
    a. 0.2
    b. 0.38
    c. 0.625
    d. 0.5o

    Thanks in Advance!
    Answer is 0,2

    1 min= 60seconds

    red signal = 30 sec. 30/60= 0,5000
    yellow signal = 5 sec. 5/60= 0,0833
    green signal = 25 sec. 25/60= 0,4167

    10 cars = 100% or 1
    4 cars = 40% or 0,4 (4/10)

    Red signal AND four cars = 0,5x0,4= 0,2 or 20%

  3. #3
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    Re: Traffic light probability question.Need help!!


    Hi,
    You could look at this as a set of 10 trials, as each car tries to pass the light. The probability of being stopped by the red light is 0.5 for each car so, the probability of exactly 4 cars being stopped out of 10 will be C(4,10)*p*(1-p) = 0.205 where C(4,10) is the combination of 4 elements taken from 10 and p is 0.5.

    regards
    rogojel

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