The shortest route from London to Cambridge is 60 miles. A lorry is expected to take 1.5 hours to travel this route. The lorry actually travels by a different route which increases the distance by 20%, but it still arrives in 1.5 hours. By how many more mph than the expected speed does the lorry travel?

8 mph

Step-by-step explanation:

The lorry's shortest route:

60 miles in 1.5 hours

speed = distance/time = (60 miles) / (1.5 hours) = 40 mph

The longer route:

time = 1.5 hours

distance = 20% more than 60 miles = 1.2 * 60 miles = 72 miles

speed = distance/time = (72 miles) / (1.5 hours) = 48 mph

Difference in speeds: 48 mph - 40 mph = 8 mph