posted by Ephraim .
Find the average speed for the journey:
jonas drives 70km in 45 min and then another 120km in 1 hour.
70*3/4 + 120*1
above is the distance travelled in 1.75 hours (1 hour, 45 minutes.) if we want the average speed, we want it 'per 1 hour'.
to get this, we divide the above answer(172.5 km) by 1.75. This gives us: