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Math Help - Speed & Distance word problems

  1. #1
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    Speed & Distance word problems

    I'm really confused. The formula for calculating distance is d=rXt. However, when using this formula my answers are wrong.

    You spot a car traveling 105 miles per hour. How far does it travel in 10 minutes?
    D= 105 X .10 my answer: 10.5 miles. However, the correct answer is 17.5 miles

    You are traveling 75 miles per hour on the interstate. How long will it take you to travel
    15 miles?
    15= 75X T
    15/75= 0.2 or 20 minutes? However, the correct answer is 12 minutes

    How far does a tractor trailer truck traveling 80 miles per hour go in 21 minutes?
    D= 80 X .21
    16.8 Miles However, the correct answer is 28 miles.

    I'm not simply looking for the answer because I already have it. I'm just trying to figure out why I have these questions wrong. Any help would be greatly appreciated. Thanks


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  2. #2
    Member Goku's Avatar
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    Re: Speed & Distance word problems

    D= 105 X .10 my answer: 10.5 miles. However, the correct answer is 17.5 miles
    10 min = 10/60 hours = 1/6 hour --- There are 60 minutes in an hour.

    D = 105 x 1/6 = 17.5

    Now try the rest...
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  3. #3
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    Re: Speed & Distance word problems

    Thanks so much. You really helped. So 21 minutes is actually 21/60 which reduces to 7/20. Is there any way you can help me in the second question. I'm still not sure how that works. I feel like I'm using the formula right but I still get the wrong answer
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  4. #4
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    Re: Speed & Distance word problems

    You are traveling 75 miles per hour on the interstate. How long will it take you to travel
    15 miles?
    15= 75X T
    15/75= 0.2 or 20 minutes? However, the correct answer is 12 minutes

    How far does a tractor trailer truck traveling 80 miles per hour go in 21 minutes?
    D= 80 X .21
    16.8 Miles However, the correct answer is 28 miles.

    I'm not simply looking for the answer because I already have it. I'm just trying to figure out why I have these questions wrong. Any help would be greatly appreciated. Thanks
    0,2 is not 20 minutes, its 0,2 of an hour or 1/5 of an hour, which is 60/5 = 12
    you are multiplying it with 0,21, what is wrong, hour got 60 minutes, so its not 21/100 its 21/60, 21/60 = 0,35, 80 x 0,35 = 28
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  5. #5
    Forum Admin topsquark's Avatar
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    Re: Speed & Distance word problems

    Oopsie!

    -Dan
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