SOLUTION: Two cars leave City A st the same time to travel to City B. One car travels at 72 km/h and other at 78 km/h. If the slower car arrives 20 min. after the faster car, how far apart a

Algebra ->  Coordinate Systems and Linear Equations  -> Linear Equations and Systems Word Problems -> SOLUTION: Two cars leave City A st the same time to travel to City B. One car travels at 72 km/h and other at 78 km/h. If the slower car arrives 20 min. after the faster car, how far apart a      Log On


   

Question 207910: Two cars leave City A st the same time to travel to City B. One car travels at 72 km/h and other at 78 km/h. If the slower car arrives 20 min. after the faster car, how far apart are City A and City B?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
Two cars leave City A st the same time to travel to City B.
One car travels at 72 km/h and other at 78 km/h.
If the slower car arrives 20 min. after the faster car, how far apart are City A and City B?
:
let d = distance between the cities
;
Write a time equation: time = dist%2Fspeed
;
convert 20 min to 1%2F3 hr
:
Slow car time = Fast car time + 20 min
d%2F72 = d%2F78 + 1%2F3
:
multiply by 2808, (half of 72*78)
2808*d%2F72 = 2808*d%2F78 + 2808*1%2F3
:
Cancel the denominators and you have:
39d = 36d + 936
;
39d - 36d = 936
;
3d = 936
d = 936%2F3
d = 312 km between cities
:
:
Check solution by finding the time difference
312/72 = 4.33 hrs
312/78 = 4.00 hrs
------------------
differ = .33 hrs ~ 20 min