title: Calculating subnet mask
body: <p>I have problem calculating a subnet mask.</p>
  
  <p>Suppose xyz college is planning to setup a small private network with network address <code>192.168.20.0</code>. The number of departments in the college are 7 and the max no. of host in each department is 25. How to calculate subnet mask?</p>
  
  <p>When I tried to google to find a tutorial for calculating such kind of problems, got nothing.</p>