Quote from panzerman:
Look, only one of three outcomes is possible in a strangle:
1) The price of the underlying is above the higher strike at expiration
2) The price of the underlying is below the lower strike at expiration
3) The price of the underlying is between both strikes at expiration
There is a 30% chance that either 1 or 2 will occur, and a 40% chance of 3 occuring. Both 1 and 2 cannot occur at the same time.
However, until expiration, the path that the price takes could very well move it below the lower strike and then all the back up above the higher strike. The probabilites only predict what will happen at the time of expiry. For an IC, the math is the same to figure the probabilities between the long and short leg.