Solution: (1) As can be seen from the table, every time you spend money in 0.8 yuan by bus, there will be 50% 3.2 yuan after the fourth bus ride.
So the balance on the card after the fifth ride is 50-3.2-0.8 = 46 yuan;
(2) According to the analysis of (1), every time you spend time in 0.8 yuan by bus,
Then n = 50-0.8m；;
(3) When m= 13 and n = 50-0.8× 13 = 39.6,
That is, Li Ming left 39.6 yuan after taking the 13 bus;
(4) According to (2), n = 50-0.8m,
When n=0, the solution is m=62.5.
So multiply it by 62 times at most (by tail cutting method).