Question

By law, the maximum slope of a wheelchair ramp is 1/12.

Answer 1

$\bf slope\implies \cfrac{\stackrel{\stackrel{rise}{height}}{4}}{\stackrel{\stackrel{run}{base}}{50}}\implies \cfrac{2}{25}\ne \cfrac{1}{12} \\\\\\ \textit{one could adjust the height}\qquad \cfrac{h}{50}=\cfrac{1}{12}\implies h=\cfrac{50}{12}\implies h=4\frac{1}{6} \\\\\\ \textit{or one could adjust the base}\qquad \cfrac{4}{b}=\cfrac{1}{12}\implies 48=b$

Answer 2

Slope is defined as rise (height) over run (length) so we can express this as slope = Height/Length. 

Your rule says that the maximum slope (H/L) cannot exceed 1/12.  If the height is 4 this means the length must be at least 4(12) = 48. 

In other words:  slope = H/L = 4(1)/4(12) = 4/48 = 1/12 

If L is less than 48 the the slope is Greater than 1/12 and this is not allowed.  Any length longer than 48 and the slope is less than 1/12 and this is OK. 

Since 50 > 48 the ramp will be acceptable