Question 232767
Pairs of markings a set distance apart are made on highways so that police can detect drivers exceeding the speed limit.
 Over a fixed distance, the speed R varies inversely with time T.
 In one particular pair of markings, R is 45 mph when T is 6 seconds.
 Find the speed of a car that travels the given distance in 5 seconds.
:
Speed varies inversely with time so we can write an inverted ratio equation, find r
{{{5/6}}} = {{{45/r}}}
Cross multiply
5r = 6 * 45
:
5r = 270
r = {{{270/5}}}
r = 54 mph if he passes the markers in 5 sec