In a certain engineering research and development company, apart from the sup- port staff which number 25, all other employees are either engineers or statisticians or both. The total number of employees (including the support staff) is 100. Of these, 50 are engineers, and 40 are statisticians; the number of employees that are both engineers and statisticians is not given. Find the probability that an employee chosen at random is not one of those classi?ed as being both an engineer and a statistician.