Answer: 9 : 50
Explanation:
There were 3,600 athletes and 20,000 volunteers.
Ratio of the number of athletes to the number of volunteers;
3,600 : 20,000
Taking that to the simplest form;
Divide by 100
3,600/100 : 20,000/100
36 : 200
Divide by 4
36/4 : 200/4
9 : 50