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Homework Help: Form an equation in terms of x

  1. Apr 28, 2010 #1
    Can anyone give some help on how I should go about creating a formula for this problem?

    Bob creates a new shade of paint by mixing black, red and white paint.
    He uses x litres of black paint.
    He uses 5 times as many litres of red paint than he uses of black paint.
    He uses 12 more litres of white paint than he uses of red paint.
    Altogether he produced 672 litres of the new shade of paint.
    Form an equation in terms of x and solve it to find the number of litres of each of the three different colours of paint used.

    Do I use different letters for the red and white paint or is it ok to call them 5x and 5(x + 12 )
  2. jcsd
  3. Apr 28, 2010 #2


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    You could do it either way but it is simplest to use the single "x". Assuming that you mean x to be the amount of black paint in litres (and you should always state that explicitely), then the amount of red paint is 5x and the amount of white paint is 12 litres more that that, 5x+ 12, NOT 5(x+ 12).

    Now add those together and set it equal to 672. Solve that equation for x and then find x+ 12 and 5x+ 12. Write the answers in full sentences- "He used 24 litres of black paint", not "x= 24" (That is not necessarily the correct answer, I just made it up.).
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