Question 758091
A car traveling at 70 kilometers per hour is passed by a second car
 going in the same direction at a constant speed.
 After 30 seconds, the two cars are 500 meters apart.
 Find the speed of the second car.
:
let s = speed of the passing car
:
We're working km/hr:
 change 500 m to {{{1/2}}} km
 change 30 sec to {{{1/120}}} hrs
:
Write a distance equation; dist = speed * time
:
Passing car dist - 70 km/hr car dist = 500 meters
{{{1/120}}}s - {{{1/120}}}(70) = {{{1/2}}}
multiply eq by 120 to cancel the denominators, results:
1s - 1(70) = 120*{{{1/2}}}
s - 70 = 60
s = 60 + 70
s = 130 km/hr speed of the passing car
;
:
Confirm this by finding the distance each car traveled
{{{1/120}}}*130 = 1.08 km
{{{1/120}}}* 70 =  .58 km
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difference in dist: .5 km which is 500 m