Question 301604
The 2 cars and their starting point form a right triangle
One leg is {{{15}}} mi
Call the north leg {{{x}}}
Then the distance between the cars is {{{5 + x}}}
{{{x^2 + 15^2 = (x+5)^2}}}
{{{x^2 + 225 = x^2 + 10x + 25}}}
{{{10x = 225 - 25}}}
{{{10x = 200}}}
{{{x = 20}}}
The northbound car had gone 20 mi
check:
{{{x^2 + 15^2 = (x+5)^2}}}
{{{20^2 + 15^2 = (20+5)^2}}}
{{{400 + 225 = 625}}}
{{{625 = 625}}}
OK