Sum[(90 choose 10)/(100 choose 10)/10+2(10 choose n)(90 choose (10-n))/(100 choose 10),{n,1,10}]

Uh oh! Wolfram|Alpha doesn't run without JavaScript.

Please enable JavaScript. If you don't know how, you can find instructionshere.Once you've done that, refresh this page to start using Wolfram|Alpha.