greatbattle, i can't see anything wrong with your calculation other than you have used a rounded figure of 30ft per 1mb (which is used for simplicity)
chchflyboy
if you think about what makes the 300ER wings longer, then u will be able to spot the difference
as for the difference between 200 and 300, counting the doors is a very easy way to tell, and if you look at enough pictures of the 200 and 300, you will see the difference clear enough
