91Ó°ÊÓ

In the following exercises, perform the indicated operation and simplify.

$\frac{{\displaystyle \frac{1}{m}}-{\displaystyle \frac{1}{n}}}{{\displaystyle \frac{1}{n}}+{\displaystyle \frac{1}{m}}}$

In the following exercises, solve each equation.

$\frac{1}{2}+\frac{2}{7}=\frac{1}{x}$

In the following exercises, solve each equation.

$\frac{5}{y-6}=\frac{3}{y+6}$

In the following exercises, solve each equation.

$\frac{1}{z-5}+\frac{1}{z+5}=\frac{1}{z^2-25}$

In the following exercises, solve each equation.

$\frac{t}{4}=\frac{3}{5}$

In the following exercises, solve each equation.

$\frac{2}{r-2}=\frac{3}{r-1}$

If yvaries directly with x, and $x=5\mathrm{when}y=30$ when, find x when $y=42$.

If yvaries inversely with x and $x=6\mathrm{when}y=20$, find$y\mathrm{when}x=2$

If yvaries inversely with the square of $x\mathrm{and}x=3\mathrm{when}y=9$, find$y\mathrm{when}x=4$.

The recommended erythromycin dosage for dogs, is 5 mg for every pound the dog weighs. If Daisy weighs 25 pounds, how many milligrams of erythromycin should her veterinarian prescribe?