This is the correct average velocity for the entire trip.

[pillar]

1.Starting from home, you bicycle 24km north in 2.5 h and then turn around and pedal straight home in 1.5h. c)What's the average velocity for the homeward leg of the trip? e)What's the average velocity for the trip?

Equations V=x/t & avg. V=(V+V initial)(1/2)

 

[G01]

You must make some attempt at the problem to get help on Physics Forums:

https://www.physicsforums.com/showthread.php?t=94379

Where are you getting stuck? What are your thoughts on the problem? What concepts/formulas do you think apply, etc?

 

[pillar]

c) 24km/1.5h=16km/h
e)((24km/2.5)+16km/h)/2=12.8km/h

 

[G01]

Part c is correct.

For part e) you are incorrectly using the formula you listed. You are off by a few decimal places. Start from the definition of average velocity:

$$v_{avg}=\frac{d_{total}}{t_{total}}=\frac{48km}{4h}=12km/h$$