Algebra · real student question

Solve x divided by (0.33668 + x) equals 0.95, for x.

Question

Solve for xx:

x0.33668+x=0.95\frac{x}{0.33668+x}=0.95

Step-by-step solution

  1. Recognise the structure. The equation says xx makes up 95%95\% of the total 0.33668+x0.33668+x. So the fixed amount 0.336680.33668 is the remaining 5%5\%, and the answer should be 955=19\frac{95}{5}=19 times it. Predicting the factor 1919 gives a target to check the algebra against.

  2. Clear the denominator. The denominator is nonzero for any solution, so multiply through:

    x=0.95(0.33668+x)x=0.95(0.33668+x)

  3. Distribute.

    x=0.319846+0.95xx=0.319846+0.95x

    since 0.95×0.33668=0.3198460.95\times 0.33668=0.319846.

  4. Collect the xx terms. Subtract 0.95x0.95x from both sides:

    x0.95x=0.3198460.05x=0.319846x-0.95x=0.319846\quad\Rightarrow\quad 0.05x=0.319846

    That coefficient 0.050.05 is precisely the 5%5\% that xx is not; the smaller it is, the larger xx becomes.

  5. Divide and confirm the predicted factor.

    x=0.3198460.05=6.39692x=\frac{0.319846}{0.05}=6.39692

    and indeed 19×0.33668=6.3969219\times 0.33668=6.39692, matching step 1 exactly.

  6. Check by substitution. The total is 0.33668+6.39692=6.73360.33668+6.39692=6.7336, and

    6.396926.7336=0.95\frac{6.39692}{6.7336}=0.95

    exactly, so x=6.39692x=6.39692.

Answer

x=19×0.33668=6.39692x=19\times 0.33668=6.39692

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