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Math Help - Ratio of 3 things

  1. #1
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    Ratio of 3 things

    To make FoundaMix concrete I need cement, sand, and aggregate mixed in the ratio 2 : 5 : 7. I need 7 tonnes of concrete for a driveway. How much of each material should I buy?

    ---------------
    I need some help please.
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    Re: Ratio of 3 things

    Quote Originally Posted by joshuaa View Post
    To make FoundaMix concrete I need cement, sand, and aggregate mixed in the ratio 2 : 5 : 7. I need 7 tonnes of concrete for a driveway. How much of each material should I buy?

    ---------------
    I need some help please.
    you have 7 tonnes divided in 2parts + 5 parts + 7 parts = 14 parts (total), 7 tonnes/14 parts =

    what would you do next?

    dokrbb
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  3. #3
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    Re: Ratio of 3 things

    Joshua

    if x = cement ,y = sand z = aggregate then x/2 = y/5 = z/7 then each ratio is equal to (x+y+z)/(2+5+7) = 7000/14 = 500
    then x/2 =500 y/5 = 500 z/7 = 500 .......cross multiply to find x,y,z.................1000,2500,3500.............. .......
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  4. #4
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    Re: Ratio of 3 things

    still have no Idea. Please, go on....
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  5. #5
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    Re: Ratio of 3 things

    How did you get the 7000?
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    Re: Ratio of 3 things

    Quote Originally Posted by joshuaa View Post
    still have no Idea. Please, go on....
    before going on..., can you tell me what you understood from what I posted, and what means the result you obtain from the fraction I provided you with?

    dokrbb
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  7. #7
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    Re: Ratio of 3 things

    Why would I add the parts, then divide the 7 into them? How am I going to benefit from this fraction?
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    Re: Ratio of 3 things

    Quote Originally Posted by joshuaa View Post
    Why would I add the parts, then divide the 7 into them? How am I going to benefit from this fraction?
    not 7 but 7 tonnes, so did you?
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  9. #9
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    Re: Ratio of 3 things

    It seems that my Basics of Ratio needs some extra skillS. Even if 7/14 = x/2, 14x = 14, x = 1 which meanS I need 1 tonne of cement, I am still confused of why I add the ratios together, then divide the needed tonnes (7 tonnes) into them!
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  10. #10
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    Re: Ratio of 3 things

    Quote Originally Posted by joshuaa View Post
    It seems that my Basics of Ratio needs some extra skillS. Even if 7/14 = x/2, 14x = 14, x = 1 which meanS I need 1 tonne of cement, I am still confused of why I add the ratios together, then divide the needed tonnes (7 tonnes) into them!
    look, you have an amount of something (in our case 7 tonnes) which you have to divide in 2 part : 5 part :7 parts, which would be a total of 14 parts of that something,

    7/14 = 0,5 (of something - in our case is 0,5 tonnes, or 500kg of something)

    now you sum them up proportionally as it is required: (2 parts x 0,5) : (5 parts x 0,5) : (7 parts x 0,5), gives you 1 tonne : 2,5 tonnes : 3,5 tonnes,

    do you get now?

    dokrbb
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  11. #11
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    Re: Ratio of 3 things

    remember the simple rule that if we want to divide a quantity V in the ratio say a:b:c:d:e etc. then each component is got by dividing the ratio by the sum of the ratios and multiplying it by the quantity. In this case the quantity of component with the ratio b will be [ b/(a+b+c+d+e)] * V
    In the given question similarly you can get the quantity of cement = (2/14)*7 Tonnes etc
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