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Math Help - Solving systems of linear equations

  1. #1
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    Solving systems of linear equations

    Doctors often prescribe the same drugs for children as they do for adults. If "a" is the age of a child and "D" is the adult dosage, then to find the child's dosage "d", doctors can use the formula
    d = D(a+1)/24 (Cowling's rule) or d = 0.08aD (Fried's rule). For what age do the two formulas give the same child's dosage?


    I know the answer is 1.1, but I don't know how to get to this answer not using a graphing calculator.
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  2. #2
    Member SengNee's Avatar
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    Quote Originally Posted by vidalex View Post
    Doctors often prescribe the same drugs for children as they do for adults. If "a" is the age of a child and "D" is the adult dosage, then to find the child's dosage "d", doctors can use the formula
    d = D(a+1)/24 (Cowling's rule) or d = 0.08aD (Fried's rule). For what age do the two formulas give the same child's dosage?


    I know the answer is 1.1, but I don't know how to get to this answer not using a graphing calculator.
    Cowling's rule:
    d_c=\frac{D(a+1)}{24}

    Fried's rule:
    d_f=0.08aD

    Given, the same child's dosage

    Therefore, d_c=d_f
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  3. #3
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    Quote Originally Posted by vidalex View Post
    ...d = D(a+1)/24 (Cowling's rule) or d = 0.08aD (Fried's rule). For what age do the two formulas give the same child's dosage?

    I know the answer is 1.1, but I don't know how to get to this answer....
    Since each is equal to "d" and since you need to find the age "a", then set them equal:

    . . . . .[D(a + 1)]/24 = 0.08aD

    You can start the solution by dividing through by D. Then solve the resulting linear equation by whatever methods they have taught you.
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