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  1. #1
    rcs
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    average speed

    Tom drove for 3 hours at 30 km/hr and another 2 hrs at 70km/h. What was his average speed for the journey?


    attempt:

    using S = d/t

    Given: 2 hrs at 70km/h and 3 hrs at 30km/h

    Solve: 30/3 + 70/2 = (10 + 35 ) /2 = 45/2 = 22.5 km/h

    please correct me if im wrong.
    because im not so sure with my solution.

    thanks
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  2. #2
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    Re: average speed

    Yes, you are wrong.
    How far does he travel in the first 3 hours ?
    How far does he travel in the next 2 hours ?
    What is his total distance travelled ?
    What is the total time taken ?
    What is his average speed ?
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  3. #3
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    Re: average speed

    Quote Originally Posted by BobP View Post
    Yes, you are wrong.
    How far does he travel in the first 3 hours ?
    How far does he travel in the next 2 hours ?
    What is his total distance travelled ?
    What is the total time taken ?
    What is his average speed ?

    What was his average speed for the journey?

    is only ask... but may i know how it is solved ...
    thanks
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    Re: average speed

    Answer Bob's questions and you will have your answer.
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    rcs
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    Re: average speed

    3(30) + 2(70) = 90 + 140 = 230 km total
    5 hrs also in total

    230/5 = 46

    so it is 46 km/hr is the answer..

    can anyone check my solution because im so sure with my answer


    thanks
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    Re: average speed

    Quote Originally Posted by rcs View Post
    What was his average speed for the journey?

    is only ask... but may i know how it is solved ...
    thanks
    By using the formula you wrote in your first post- average speed is the distance traveled divided by the time. And those are given by answering the questions in the first response.
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  7. #7
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    Re: average speed

    how come and how it is really done?
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    Re: average speed

    Quote Originally Posted by rcs View Post
    how come and how it is really done?
    The equation for average speed is based on the total distance over the total time. So v_{ave} = \frac{\text{total distance}}{\text{total time}} = \frac{d}{t}

    -Dan
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  9. #9
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    Re: average speed

    Quote Originally Posted by rcs View Post
    3(30) + 2(70) = 90 + 140 = 230 km total
    5 hrs also in total

    230/5 = 46

    so it is 46 km/hr is the answer..

    can anyone check my solution because im so sure with my answer


    thanks
    This is correct.
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