Bill made a trip to the train station and back. The trip there took six hours and the trip back took four hours. He averaged 45 km/h on the return trip. Find the average speed of the trip there.
Let's first start off with a knowledge of what "average speed" actually is. Average speed is defined as:
total distance / total time
The distance to the train station is equal to 45 * 4km, which is how far he traveled on the return trip(45 km per hour for 4 hours). That means that the distance for one trip is equal to 180 km. Since we only need total distance / total time, the total distance is equal to the distance of one trip multiplied by 2, which is 180*2 = 360. Then, total time is just 6 hours + 4 hours, which is 10 hours.
360 / (6+4) = 360 / 10 = 36 km/h
Here's another way to put it:
Since we know that Bill traveled 4 hours, we can do 45*4 which would be 180 for one trip.
We need to find out the (total distance)/(total time).
The total distance, or round trip is just multiplying one trip by 2. That will get us 180*2 = 360.
The total time, as we know, is 10 hours.
From now it is easy: 360/10=36
Bill traveled with an average speed of 36km/h on the way there.
Hope this helped!