MEI runs an 18 miles course at a constant speed. If she doubles her usual speed, she can complete the course in an hour and a half less than her usual time. what is Mei's usual speed and her usual time to complete the course?
-
At her usual speed:
v.t =18 (1)
If she doubles her speed:
2v( t-1,5)=18 (2)
From (1) v =18/t (3)
Substituting (3) in (2):
2.18/t(t-1,5) = 18
36 - 54/t = 18
36t -54 = 18t
18t=54
t= 3 hs ----> usual time
v= 18/t ==> v=18/3 = 6 miles/h ----> usual speed
v.t =18 (1)
If she doubles her speed:
2v( t-1,5)=18 (2)
From (1) v =18/t (3)
Substituting (3) in (2):
2.18/t(t-1,5) = 18
36 - 54/t = 18
36t -54 = 18t
18t=54
t= 3 hs ----> usual time
v= 18/t ==> v=18/3 = 6 miles/h ----> usual speed
-
If half the speed is 90 minutes, then the time she would take with the usual speed is 180 minutes.
180 minutes = 18 miles
Divide everything by 3 to get 60 minutes (MPH)
60 Minutes = 6 Miles
The usual speed is 6 miles per hour and normally she would take 3 hours to run 18 miles. If she doubles her speed (12 miles) she would take 1 hour and 30 minutes (90 minutes less than with her usual speed).
180 minutes = 18 miles
Divide everything by 3 to get 60 minutes (MPH)
60 Minutes = 6 Miles
The usual speed is 6 miles per hour and normally she would take 3 hours to run 18 miles. If she doubles her speed (12 miles) she would take 1 hour and 30 minutes (90 minutes less than with her usual speed).