TITLE: Finding the average speed plus a break
QUESTION [0 upvotes]: I have the following equation when the driver drove 2.5h at 120 km/h and then stopped for 30 minutes. Then he drove for 20 minutes at 25 m/s.
The result of the equation is to determine the average speed.
When using the formula s = v.t, I cannot set a 30-minute pause. I tried to use the formula v = s / t where s = 2.5 + 0.3 + 0.5 and t = 120 + 90 + 0. I tried to define the break as 0 km/h in 30 minutes, unfortunately this is not in my formula.
How do I add a pretense to the formula?

REPLY [2 votes]: Advice: don't rely on mechanically applying a formula. Think about what is actually happening in the problem instead.
The average speed for a journey is total distance travelled divided by total journey time. So we need to find the total distance travelled and the total journey time.
The total time for the journey is $2.5$ hours plus $30$ minutes plus $20$ minutes, which is $3$ hours and $20$ minutes, or $\frac {10}{3}$ hours.
The distance travelled in the first part of the journey is $2.5 \times 120 = 300$ km.
The distance travelled in the second part of the journey is $1200 \times 25 = 30000$ metres, or $30$ km.
So the total distance travelled is $330$ km.
Now you have all the information that you need to solve the problem.
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