Question 472793
The formula r=2√5L can be used to approximate the speed r, in miles per hour,
 of a car that's left skid marks length L, in feet.
 How far will a car skid at 20 mph?
:
Replace r with 20 in the given formula
{{{2sqrt(5L)}}} = 20
Square both sides
4(5L) = 20^2
20L = 400
L = {{{400/20}}}
L = 20 mph with 20' skid mark