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Math Help - Need to find formula

  1. #1
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    Need to find formula

    Because tsunamis travel very quickly, warning people of an approaching tsunami can be difficult. In 1998, some mexican scientists developed a new method of measuring earthquakes and predicting tsunamis. Before 1998, it took 20 minutes to determine whether and earthquake would produce a tsunami. With the new technology te task may be completed in 5 minutes. What percentage decreases in time is this ?



    Thanks, Chhoeuk
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  2. #2
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    Quote Originally Posted by chhoeuk View Post
    Because tsunamis travel very quickly, warning people of an approaching tsunami can be difficult. In 1998, some mexican scientists developed a new method of measuring earthquakes and predicting tsunamis. Before 1998, it took 20 minutes to determine whether and earthquake would produce a tsunami. With the new technology te task may be completed in 5 minutes. What percentage decreases in time is this ?

    Thanks, Chhoeuk
    Hi,

    the absolute decrease of time: 15 min

    Let p be the percentage you are looking for. Then use the proportion:

    15/20 = p/100 ===> p = 75%

    EB
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