How many planets are there that we know of and how many do you think our undiscovered?

Question: How many planets are there that we know of and how many do you think our undiscovered?
- Keywords:
  discovery,
  planet,
  universe
Asked by Grace to Anna, George, Rob, Stefan on 20 Nov 2014.
- Stefan Lines answered on 20 Nov 2014:
  
  As of today we know of 1850 planets. We think that there are as many as 40 billion Earth like planets in the habitable zone – so it seems like there are trillions of planets undetected – just in our galaxy (of which there are about 100 billion in the universe). Wow.

Question: How many planets are there that we know of and how many do you think our undiscovered?