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Thread: Average Speed

  1. #1
    Super Member harpazo's Avatar
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    Average Speed

    What exactly is average speed? Can you provide an example?
    Is the formula r = D/t?
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  2. #2
    Member Walagaster's Avatar
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    Re: Average Speed

    Quote Originally Posted by harpazo View Post
    What exactly is average speed? Can you provide an example?
    Is the formula r = D/t?
    That formula can be used in this sense: If you traveled $D$ miles in time $t$ hours, you could say your average speed for the trip was $r = D/t$. That measure doesn't take into account any time taken for any stops or changes in speed along the way, but it does tell you that if you had traveled at exactly that average speed for the whole trip, you would get there in the same $t$ hours. If you have varying velocity it becomes a calculus problem.
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  3. #3
    Super Member harpazo's Avatar
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    Re: Average Speed

    Quote Originally Posted by Walagaster View Post
    That formula can be used in this sense: If you traveled $D$ miles in time $t$ hours, you could say your average speed for the trip was $r = D/t$. That measure doesn't take into account any time taken for any stops or changes in speed along the way, but it does tell you that if you had traveled at exactly that average speed for the whole trip, you would get there in the same $t$ hours. If you have varying velocity it becomes a calculus problem.
    Can you give me an actual average speed word problem at the algebra 2 level not calculus?
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    Re: Average Speed

    "If it took you two hours to walk a distance of six miles what was your average speed during the walk?"
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  5. #5
    Junior Member Cervesa's Avatar
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    Re: Average Speed

    A cyclist rides a distance of 10 miles from point A to B in half an hour. The return trip from B to A with the wind at her back takes 20 minutes.

    What is her average speed for the round trip in miles per hour?

    Spoiler:
    24 mph
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  6. #6
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    Re: Average Speed

    Quote Originally Posted by Cervesa View Post
    A cyclist rides a distance of 10 miles from point A to B in half an hour.
    The return trip from B to A with the wind at her back takes 20 minutes.

    What is her average speed for the round trip in miles per hour?
    Harpazo, do you "see" that solution to above is simply: (10 + 10)/(1/2 + 1/3) ?
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  7. #7
    Super Member harpazo's Avatar
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    Re: Average Speed

    Quote Originally Posted by Zexuo View Post
    "If it took you two hours to walk a distance of six miles what was your average speed during the walk?"
    D = rt

    Solve for r.

    D/t = r

    6/2 = r

    3 = r

    The average speed is 3 miles per hour.
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  8. #8
    Super Member harpazo's Avatar
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    Re: Average Speed

    Quote Originally Posted by DenisB View Post
    Harpazo, do you "see" that solution to above is simply: (10 + 10)/(1/2 + 1/3) ?
    Yes, I do.
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  9. #9
    Super Member harpazo's Avatar
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    Re: Average Speed

    Quote Originally Posted by Cervesa View Post
    A cyclist rides a distance of 10 miles from point A to B in half an hour. The return trip from B to A with the wind at her back takes 20 minutes.

    What is her average speed for the round trip in miles per hour?

    Spoiler:
    24 mph
    Let A = average speed for round trip.

    A = (10 + 10)/(1/2 + 1/3)

    A = (20)/(5/6)

    A = 20 • (6/5)

    A = 4 • 6

    A = 24 miles per hour
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    Re: Average Speed

    Quote Originally Posted by harpazo View Post
    Let A = average speed for round trip.

    A = (10 + 10)/(1/2 + 1/3)

    Here 10 + 10 = 10miles +10 miles = 20 miles ; 1/2 +1/3 =1/2 hours + 1/3 hours = 5/6 hours. You don't need to write in the units, I'm just trying to point out that what you have done is good because the units match up (see other posts for when you do not do this)

    A = (20)/(5/6) Units here are miles in numerator and hours in denominator = miles/hour or mph

    A = 20 • (6/5)

    A = 4 • 6

    A = 24 miles per hour
    Perfect. See my comment in red above about units.
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  11. #11
    Super Member harpazo's Avatar
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    Re: Average Speed

    Quote Originally Posted by Debsta View Post
    Perfect. See my comment in red above about units.
    Let's give total credits to DenisB who created what needed to be calculated. I just basically did the math but his help was needed.
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