Question 967395

A car travels 120 miles. A second car traveling 10 mph faster than the first car.makes the same trip in 1 hr less time. Find speed of each car.
<pre>Let speed of slower car be S
Then speed of faster car is: S + 10
We then get: {{{120/S = 120/(S + 10) + 1}}}
{{{120(S + 10) = 120S + S(S + 10)}}} ------- Multiplying by LCD, S(S + 10)
{{{120S + 1200 = 120S + S^2 + 10S}}}
{{{S^2 + 120S + 10S - 120S - 1200 = 0}}}
{{{S^2 + 10S - 1200 = 0}}}
(S - 30)(S + 40) = 0 
S, or speed of slower car = {{{highlight_green(30)}}} mph        OR         S = - 40 (ignore)
Speed of faster car: 30 + 10, or {{{highlight_green(40)}}} mph