If a student leaves home at 7:30 AM to walk to his school 2 km away, stops at a neighbor's house for 15 min, then arrives at school at 8:00 AM, what is the student's average speed for the trip to school?

Speed is a quantity that relates the displacement that an object makes in a given unit of time. In other words, speed is a physical quantity that expresses the relationship between the space traveled by an object, the time used for it and its direction.

Since the average speed relates the change in position to the time taken to effect said change, then:

[tex]speed=\frac{change in position}{time}[/tex]

In this case, the student travels a total distance of 2 km between his home and school and the total time spent on the trip is 30 minutes, then:

change in position= 2 km
time= 30 minutes= 0.5 hours (being 60 minutes = 60 hours)

Replacing:

[tex]speed=\frac{2 km}{0.5 hours}[/tex]

Solving:

speed= 4[tex]\frac{km}{hours}[/tex]

The student's average speed for the trip to school is 4 [tex]\frac{km}{h}[/tex]