Well, you are right that the number of employees can range from 1 to infinity. However, according to condition 1 and 2, only 35 percent of the projects can have number of employees ranging from 1 to 2 and 25 percent of projects can have employees ranging from 4 to n. The remaining 40 percent of the projects will have 3 employees.
When the number of employees are arranged in ascending order, irrespective of what their values are and that can range from 1 to infinity, 3 will fall in the middle and hence will be the median.