The problem is $$\frac{30}{4x+5} = 95$$ I multiplied $95$ by $(4x+5)$ and then eventually got: $$-445 = 380x$$ and dividing by $380$ gives $x = -1.17$. Is this correct?
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Just to be sure: you mean $\frac{30}{4x + 5}$ and not $\frac{30}{4x} + 5$? Yes, no, maybe? – Robert Soupe Aug 10 '14 at 17:43
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Looks correct to me.
The reasoning is sound, and if we plug your approximation into the original equation, we obtain: $$\frac{30}{4*-1.17 + 5} = \frac{30}{0.32} = 93.75$$ which is fairly close to $95$, so this looks pretty good.
If we plug in the exact solution $x = -445/380 = -89/76$, then we get $$\frac{30}{4*(-89/76) + 5} = \frac{30}{-89/19 + 95/19} = \frac{30 \times 19}{-89 + 95} = 5 \times 19 = 95$$ which is exactly what we want. You’ve rounded correctly, so your solution is correct.
alexwlchan
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Your answer is an approximation to the correct answer of -89/76. If you are looking for an approximation then your answer is fine (to two decimal points) otherwise, reduce the fraction.
Paul Sundheim
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Yes, it's correct. The answer is $$x=-\frac{445}{380}=-\frac{89}{76}\approx -1.17.$$
mathlove
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