Posted by **Kayley** on Tuesday, October 6, 2009 at 5:40am.

a car goes at a constant speed for 120 kms, on the way back he goes at half the speed. he drives for a total of 4 hours and 30 minutes. what are the two speeds?

- algebra -
**Reiny**, Tuesday, October 6, 2009 at 7:56am
let the speed on the first trip be x km/h

then the speed on the return trip will be x/2 km/h

Time for first part = 120/x hours

and on the return trip = 120/(x/2) = 240/x hours

then 120/x + 240/x = 4.5

360/x = 4.5

x = 360/4.5

= 80

so he went 80 km/h for the first part and only 40 km/h on the way back.

check:

time for first part = 120/80 = 1.5 hrs

on way back = 120/40 = 3 hrs, for a total of 4.5 hrs.

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