Math CentralQuandaries & Queries


Question from john, a student:

Sally travels by car from one city to another. She drives for 20.0 min at 68.0 km/h, 40.0 min at 37.0 km/h, and 51.0 min at 77.0 km/h, and she spends 12.0 min eating lunch and buying gas.

What is the average speed for the trip?

Hi John,

Average speed is the total distance divided by the total time. The time is given in two different units, minutes and hours, and you need to decide which units to use. I'm going to use hours.

20 min is 20/60 = 1/3 hours,
51 min is 51/60 hours,

Add the 4 times to obtain the total time.

Distance: If she drives at 68 km/h for 1/3 hours how far does she travel?

Perform the same calculation for each of the 4 legs of the trip and add the distances to find the total distance travelled.

I hope this helps,

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