1+99/100*(1/50*80+49/50*(1/25*60+24/25*(1/12.5*40+11.5/12.5*(1/6.25*20))))

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.