Practice!

Sample Problem

Thomas drove from the urban to the country side at an average speed of 50 km/h. After traveling 60 km, he had 3/4 of the journey left. How much time would he have saved if he had travelled at an average speed of 80 km/h for the whole journey?

  h min

Solution

The total distance of the whole journey: 60 ÷ (1-3/4) =  60 ÷ 1/4 = 60 × 4 = 240 km

The time for 50 km/h: 240 ÷ 50 = 4.8 h

The time for 80 km/h: 240 ÷ 80 = 3 h

Thus, the time difference: 4.8 - 3 = 1.8 h = 1 h + 0.8 × 60 = 1 h 48 min