Answer:
33.3
Explanation:
Normally there are 4000 to 11000 WBCs in a microliter of blood averaging almost 7500. While there are 150,000 to 350,000 platelets in a microliter blood of a normal person averaging almost 250,000. Thus the ratio can be as 250,000 :7500 resulting in 33.3. If a range is to be given, it ranges from 31.8 to 37.5 per microliter of blood. 
 
        
             
        
        
        
Maybe because these particular cells die faster than other cells in the body, for example the receptors cells in your nasal cavity only lasts for about 3-4 weeks and after that it dies, therefore new news are formed every week in order to keep your nasal cavity from deteriorating your smell ability.
Some blood cells only lasts for about 120 days that's why new cells are formed and produced, faster production means faster cell division.
It depends on the type of cell and the current situation of those cells.