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Math Help - Trouble figuring out what method to use, HELP!

  1. #1
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    Trouble figuring out what method to use, HELP!

    Dear all, I don't think this is difficult, but I am stuck........

    If Steven can mix 20 drinks in 5 minutes, Sue can mix 20 drinks in 10 minutes, and Jack can mix 20 drinks in 15 minutes, how much time will it take all 3 of them working together to mix the 20 drinks?

    What method should I use? How?

    Thanks so much!
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by mak15 View Post
    Dear all, I don't think this is difficult, but I am stuck........

    If Steven can mix 20 drinks in 5 minutes, Sue can mix 20 drinks in 10 minutes, and Jack can mix 20 drinks in 15 minutes, how much time will it take all 3 of them working together to mix the 20 drinks?

    What method should I use? How?

    Thanks so much!
    Make Job/Time ratios and add up the rates.

    Let mixing 20 drinks be a job.

    Then Steven does 1/5 jobs/min,
    Sue does 1/10 jobs/min, and
    Jack does 1/15 jobs/min

    To find how long it will take them to make 20 drinks together, add up their rates.

    we have 1/5 + 1/10 + 1/15 = 11/30 = 1/(30/11)

    since the time to complete 1 job is in the denominator when 1 is in the numerator, they take 30/11 mins to complete the job together, that is roughly 2.7272 minutes
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  3. #3
    Junior Member Spimon's Avatar
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    Try finding out how many each person can make in 1 minute.
    This will then lead us to being able to find out how many the whole team can make in 1 minute.

    Alternatively you could find out how long it takes the whole team to make 1 drink and multiply this by 20.


    Steven does 20 in 5 mins or 4 per minute.
    Sue does 20 in 10 mins or 2 per minute.
    Jack does 20 in 15 mins or 4/3 per minute.

    All up they do 4+4+4/3 = 22/3 ~ 7.33 per minute.

    20/7.33 = 2.7272

    2.7272*60 = 164 seconds or 2:44mins.
    Last edited by Spimon; May 9th 2008 at 09:43 PM.
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  4. #4
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    Quote Originally Posted by Jhevon View Post
    Make Job/Time ratios and add up the rates.

    Let mixing 20 drinks be a job.

    Then Steven does 1/5 jobs/min,
    Sue does 1/10 jobs/min, and
    Jack does 1/15 jobs/min

    To find how long it will take them to make 20 drinks together, add up their rates.

    we have 1/5 + 1/10 + 1/15 = 11/30 = 1/(30/11)

    since the time to complete 1 job is in the denominator when 1 is in the numerator, they take 30/11 mins to complete the job together, that is roughly 2.7272 minutes
    Thanks for the replies, people! Can you guys explain why the right answer was 2 minutes and 44 seconds!
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  5. #5
    Junior Member Spimon's Avatar
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    2:44 seconds is the same as 2.72 minutes, just in Hr:Min form.


    2min 44 seconds = 2(60)+44 seconds = 163 seconds.
    Divide this by 60 and u get 2.72 minutes.
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  6. #6
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by mak15 View Post
    Thanks for the replies, people! Can you guys explain why the right answer was 2 minutes and 44 seconds!
    i gave you the answer. 0.727272.... minutes is 44 seconds. just multiply it by 60
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  7. #7
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    I found the answer by converted it back to 60 seconds. Thanks guys!
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