How to interpret either A or B (or both) statements in LG

[sweetygurl]

Hi,

I understand that the statement, "Either A or B" on the LSAT is inclusive of the word "or both" but when do we know that it should be interpreted accordingly?

In other words, how do we distinguish which situations call for each scenario "A only" or "B only" or possibly "A and B both"?

For example in 10/2004 LG Game III, a statement says
"The site visited 3rd dates from a more recent century than does either the site visited 1st or that 4th."
Theoretically this could lead to 3 different sketches
1) 3rd > 1st only
2) 3rd > 4th only
3) 3rd > 1st and 4th both
BUT the game discussed above actually called for the 3rd scenario. How do we figure out when to use which scenario accordingly?

Please help.
Any advice will be appreciated.

Thanks

[nbayar1212]

Any "A or B" statement can logically be interpreted to include "or both" as a third possible option.

Think of it like this: if I said you need to pack either an apple or an orange for your lunch today, and you packed BOTH an apple and an orange, you have actually fulfilled the logical requirement of the statement "pack either an apple or an orange," because you have fulfilled what i have necessarily asked of you to do i.e. bring one of the fruits.

The only time this third "or both" option is not a possibility is if the statement is qualified with a "but not both" at the end.

[MattK698]

Hi, I'm a little unsure about how to write a contrapositive of in situations such as this?

So, if the stimulus says the following: "A --> B/C/both", would the contrapositive look like the following? "-B & -C --> -A"? instead of "-B / -C --> -A".

Thank you!