There is an empty tank which needs $29$ bottles of water to fill with. The workers pour $5$ bottles of water during the day, but uses $1$ bottle of water during the night. In how many days can the tank be filled with water? 
Overseas Competition->Knowledge Point->Word Problem Modules
Every day: $5-1=4$ bottles.  $29\div4=7R1$  But for the last day, the tank can be filled with water without using during the night. 