Question 82309
distance(d)=rate(r) times time(t) or d=rt; r=d/t and t=d/r

Let r=rate of first car
Then r+15=rate of other car

Distance first car travels in 2 hours=rt=2r
Distance other car travels in 2 hours=rt=2(r+15)

Now we are told that the distance first car travels plus the distance second car travels equals 240 km.  So:

2r+2(r+15)=240  get rid of parens

2r+2r+30=240  subtract 30 from both sides

2r+2r+30-30=240-30  collect like terms

4r=210  divide both sides by 4
r=52.5 km/hr----------------------------rate of first car

r+15=52.5+15=67.5 km/hr---------------------rate of other car

CK

2(52.5)+2(67.5)=240
105+135=240
240=240


Another way to look at this problem is to note that the two cars are separating at the rate of (r+r+15) km/hr . So in 2 hrs, they will have separated 2(r+r+15) km or 2r+2r+30 and that equals 240 km---same eq as before.


Hope this helps--------------------ptaylor