Andy took a bus and then walked from his home to downtown. For the first 1.6 hour, the bus drove at an average speed of 15 km/h. For the
next 0.4 hours, he walked at an average speed of 4.5 km/h. What was
the average speed for the whole journey?

Av = 12.9 [km/h]

Explanation:

We must remember that the average speed is defined as the relationship between the space traveled over a certain time.

where:

Av = average speed [km/h]

x = distance [km]

t = time [hr]

For when he was on the bus

The distance can be calculated by clearing the equation, for the term of the distance

For when Andy was walking

Now the total time is the sum of 1.6 + 0.4 = 2 [hr], and the total distance is the sum of the distances calculated above.

The average speed is calculated using the ratio of space to time.

  distance on the y-axis and time on the x-axis.

explanation:

the instantaneous velocity = change in position/time taken

the slope of the graph should give instantaneous velocity.

  slope of a graph = change in value of y -axis / change in values of x -axis

  comparing both the equations

    change in value of y -axis = change in position

  change in values of x -axis = time taken

so position values should be on the y axis and time values should be on the x axis.

distance on the y-axis and time on the x-axis.