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Rational number word problem: cosmetics

Remember units of measurement? Convert minutes into hours and put your knowledge of fractions to work in this word problem. Created by Sal Khan.

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  • duskpin ultimate style avatar for user isabeldelagarza
    How do you figure out the cost of a meal before tax if you only have the cost after tax? This is where my practice problems told me to go when I got stuck.
    (13 votes)
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    • leaf yellow style avatar for user Ryan Y
      Well, if you have the tax %, then you could do it. All you would have to do is multiply the tax % by the total cost. You would then subtract what you got from the total cost and you would have the cost before tax.
      Hope this helps.
      (18 votes)
  • blobby green style avatar for user ryu min
    Please someone explain this for me.

    Julian is using a biking app that compares his position to a simulated biker traveling Julian's target speed. When Julian is behind the simulated biker, he has a negative position.
    Julian sets the simulated biker to a speed of 20km/h. After he rides his bike for 15 minutes, Julian's app reports a position of -2 1/4 km

    What has Julian's average speed been so far?
    (4 votes)
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    • primosaur tree style avatar for user Bradley Reynolds
      Ok so in this situation we have the rate of speed of the simulated biker (20km/h) how long the simulated biker and Julian have traveled for (15 minutes) and how far Julian is behind the simulated biker (-2 1/4 km). The first step is to figure out how far the simulated biker has gone. Speed is simply distance over time so if we multiply our simulated biker's rate by the time it has been riding we get its distance. However, our time is in minutes so we must convert it to hours. To do this we divide it by 60, which gives us 0.25 or one quarter hour. 20km per hour times 1/4 hour gives us 5km, which is the distance the simulated biker has traveled.
      Now we can figure out how far Julian has traveled, he is 2 1/4 km behind the simulated biker so 5 km - 2 1/4 km gives us Julian's distance of 2 3/4 km. Since we know Julian traveled this distance in 15 minutes his rate is (2 3/4 km)/(1/4 h) since we already know 15 minutes is a quarter hour. Now we have to get it to be over a whole hour, so we multiply the fraction by 4/4, which works because a number divided by itself is equal to 1. 2 3/4 * 4 can be done by turning 2 3/4 into the improper fraction 11/4 * 4, which gives us 44/4 km or just 11km and 1/4 h times 4 is just 1h. So our final answer of Julian's average speed is 11km/h.
      (11 votes)
  • male robot johnny style avatar for user Asher Silverman
    is there a faster way?
    (6 votes)
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  • leaf grey style avatar for user Nathan106
    I've watched every single video on Rational number word problems and I am still very confused. Can someone please help me?
    (4 votes)
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  • aqualine ultimate style avatar for user JLD
    2400mins/1 person = x mins/8 people

    (8people * 2400mins)/1 person = x mins

    Can someone explain why setting up a ratio would not work here?
    (3 votes)
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  • aqualine ultimate style avatar for user ℂ𝕒𝕣𝕠𝕝𝕪𝕟 ッ
    hii uh i dont get this .-.
    (2 votes)
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  • male robot hal style avatar for user 7AD
    How come I'm still confused after watching all of these videos to help me do "Rational Word Problem"? This makes me a little confused.
    (2 votes)
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  • blobby green style avatar for user mimiq
    Hello teacher!
    Why can't the formula t=w/r. be used in this topic?
    I think it should be t=1200/2=600min
    How should I avoid such a mistake and can you give me a tip on how to use this formula? Thank you very much!
    (My English is not my first language and I think maybe it's because of translation problems with some of the words that I don't know how to solve the questions)
    What I mean is: can you help me write down how the title asks me if I can use this formula?thank you very much!
    (2 votes)
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  • aqualine seed style avatar for user paxtonsmoore
    thanks a lot for the videos because they really help me i dont know what i would do without them :))

    yes i know sorry this is not a question but thanks

    (^-^)
    (2 votes)
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  • starky sapling style avatar for user Schuitema, Aaron
    would it really matter the amount of people there are by making the gift bags if it only took Jess only 2 minutes?
    (2 votes)
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Video transcript

Jess recently started a business producing cosmetic products made from natural ingredients. She wants to advertise her products by distributing bags of samples in her neighborhood. She calculated that it takes her two minutes to prepare each bag. How many hours-- they give us minutes here, now they want hours-- how many hours will it take to prepare 1,200 bags of samples if she asks seven friends to help her with her work? So the one thing we could think about is, how long would it take her to do it by herself? So it takes her, by herself, two minutes per bag. And then we have 1,200 bags, not 12 bags, 1,200 bags which means it's going to take her two minutes for each of the 1,200 bags. Well that's 2 times 1,200 is 2,400 minutes. Now that's if she was just working on it by herself, but she's got seven friends. And we can assume that they would all take about two minutes to prepare each bag. Now this is a little bit tricky because you might want to divide this by 7 saying, hey, we're going to have seven times as many people. But you remember, she asks seven friends so there's actually eight people involved. There's Jess and her seven friends. So it's actually going to be eight times faster than if Jess did it by herself. This is if she only had one person. If you're going to have eight people, you are going to take eight times less time. So with eight people, it's going to be 2,400 divided by 8 is 300 minutes. And we're almost done, except for the fact that they asked for our answer in terms of hours. So 300 minutes is how many hours? Well you have 60 minutes per hour so you could say 300 minutes-- I'll just write min for short-- divided by 60 minutes per hour gives us 300 divided by 60 is 5 hours. So it will take Jess and her seven friends, a total of eight people, five hours to prepare all of her sample bags.