A family have been stuck in bank holiday traffic for the last four hours. In the first hour they covered two fifths of their total journey. The next hour they covered one third of what was left. The following hour they covered one quarter of the remainder, and in the fourth hour half of the remaining distance. The family still have 20 miles left to travel. How many miles have they travelled so far?
1st hour = 2/5 of journey = 0.4 = 8 miles
2nd hour = (1/3) x (3/5) = 0.2 = 4 miles
3rd hour = (1/4) of 0.2 = 0.05 = 1 mile
4th hour = (0.005) = ½ mile
20/5 = 4 miles