In winter a train travels between two towns 264 km apart at an average speed of 72 km/h. In summer the journey takes 22 minutes less than in winter. Work out the average speed in summer.
Well first you have to work out the duration of the entire trip in winter. This is given by $\displaystyle \frac{264}{72} = 3.67$ or 3 hours and 40 mins.
The trip in summer is 22 mins less to it must take 3 hours and 18 mins (or 3.3 hours) . If the distance does not change and is still 264km and you know how long it takes, the average speed will now be a simple divsion $\displaystyle 264 \div 3.3$ hours