SOLUTION: A car travel 15KM in a city at a certain speed. outside the city it travel 72KM at twice the former speed. if the total traveling time is 1h 8min, find the average speed in the c

Question 890621: A car travel 15KM in a city at a certain speed. outside the city it travel 72KM at twice the former speed. if the total traveling time is 1h 8min, find the average speed in the city
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
A car travel 15KM in a city at a certain speed.
outside the city it travel 72KM at twice the former speed.
if the total traveling time is 1h 8min, find the average speed in the city
:
let s = speed in the city
then 2s = speed in the country
:
change 1 hr 8 min to reduces to hrs
:
Write a time equation; time = dist/speed
:
City time + country time = 1 hr 8min
+ =
multiply equation by 30s
30s* + 30s* = 30s*
cancel the denominators and you have
30(15) + 15(72) = 2s(17)
450 + 1080 = 34s
1530 = 34s
s = 1530/34
s = 45 km/h in the city
:
:
Check this by finding the time at each speed, (90 km/h in the country)
15/45 = .333 hrs
72/90 = .8 hrs
---------------
total = 1.133 hrs which is 6 hr 8 min
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