Fantasy Baseball Debate - Part 2

The optimal move here is to "Platoon" the lefties. Dave (see his comment in the previous post) is correct, the pair of lefties is the better choice, even though their overall averages are lower than the other pair. Here is an explanation in my words:

According to Chase and Dave's split stats: 215 vs LHP, 315 vs RHP, and 290 overall, you can determine that Chase and Dave must see LHP 25% of the time and RHP 75% of the time, because 215*(x) + 315*(1-x) = 290, X equals 25% and 1 minus X equals 75%.

Since Chase and Dave are on separate MLB teams, they each have a 3/4 shot at facing a RHP on any given night and there is only a (1/4)*(1/4) = 1/16 chance that they will both face LHP on any given night. So with Chase and Dave, 15/16 of the time as a manager you will be able to choose one of them that is facing a RHP that evening and 1/16 of the time you will have to choose one of them even though they are facing a LHP that evening. 15/16 of the time you can expect a 315 average out of your 3B and 1/16 of the time you will only get 215. The overall average you can then expect from your 3B slot would be (15/16)*(315) + (1/16)*(215), which is 309, which is higher than the 300 you would get out of the pair of switch hitters.

What lessons can you take from this counter-intuitive example and apply to your fantasy baseball draft strategy? Let's save that for another post