Solve $\bar{v}=\frac{240+180}{3+2}$

Step-by-step solution

1. Step 1 · Total distance
   $$d=240+180=420$$

   Average speed uses totals, not an average of the two speeds.

2. Step 2 · Total time
   $$t=3+2=5$$

   Add the two legs of the journey.

3. Step 3 · Speed = distance / time
   $$\bar{v}=\frac{420}{5}=84$$

   Averaging 80 and 90 would give 85, which is wrong because the legs differ in duration.