If y varies inversely as x and x=50 when y=2.7, find y when x=80(round the answer to the nearest tenth)
possible answers: 3.4, 0.2, 4.3 1.7
y varies inversely as x means:
$\displaystyle y=\frac{k}{x}$ where k is called the constant of proportionality.
Use your first bits of info to calculate k:
$\displaystyle 2.7=\frac{k}{50}$
$\displaystyle k=135$
Now on to your second set of info to find y when x=80.:
$\displaystyle y=\frac{135}{80}$
$\displaystyle y=1.6875\approx{1.7}$