Question 887250

Can you help me solve the problem? I need this as a guide in solving other problem.
A car travels 20 kph faster than a truck. The car covers 480 km in two hours less than the time it takes the truck to travel the same distance. How fast does the car travel? 
THANKS.
<pre>
Let the speed of the car be S
Then speed of truck is: S - 20
Time taken by car to travel 480 km: {{{480/S}}}
Time taken by truck to travel 480 km: {{{480/(S - 20)}}}
Since the car takes 2 hours less than the truck, to travel 480 km, we can say that: {{{480/S + 2 = 480/(S - 20)}}}
480(S - 20) + 2(S)(S - 20) = 480(S) ------- Multiplying by LCD, S(S - 20)
{{{480S - 9600 + 2S^2 - 40S = 480S}}}
{{{2S^2 - 480S + 480S - 40S - 9600 = 0}}}
{{{2S^2 - 40S - 9600 = 0}}}
{{{2(S^2 - 20S - 4800) = 2(0)}}}
{{{S^2 - 20S - 4800 = 0}}}
(S - 80)(S + 60) = 0
S = 80                         OR                         S = - 60 (ignore)
S, or speed of car = {{{highlight_green(highlight_green(80))}}} km/h