Answer:
 500 cm by 212.5 cm
Explanation:
Given : 
The main arena hall has dimensions 200 m by 85 m.
On a large diagram on the office wall the scale is 1:40. 
To Find: What are the dimensions of the floor space 
Solution :
Length of arena hall = 200 m 
Scale is 1:40
So, the length of the floor = 

 = 

Since 1 m = 100 cm 
So, 5 m = 100*5 = 500 cm 
Width of arena hall = 85 m
So, width of floor = 
 
 
 = 

Now 1 m = 100 cm 
So, 2.125 m = 212.5 cm
Thus the dimensions of floor is 500 cm by 212.5 cm