1-Sum[ (Binomial[10,k]*Binomial[40,10-k]/Binomial[50,10])*(Binomial[50-20+k,10]/Binomial[50,10]), {k,0,10}]

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.