"add apples and orages..."

[higurashi]

Hello,
Would someone give me the meaning of the red highlighted sentences?

I have no idea about the relationship between apples, oranges, lemon, and bananas, especially "lemon" and "bananas".

Similarly, if their comination involves arbitrary decisions, the results provide potentially misleading results. (As an aside and in a somewhat lighter vein, it is well known that, if you add apples and oranges, the answer is a lemon; but if you subtract apples from oranges, the answer can be totally bananas.)

Thank you,
Higurashi

[MikeNewYork]

Hello,
Would someone give me the meaning of the red highlighted sentences?

I have no idea about the relationship between apples, oranges, lemon, and bananas, especially "lemon" and "bananas".

Similarly, if their comination involves arbitrary decisions, the results provide potentially misleading results. (As an aside and in a somewhat lighter vein, it is well known that, if you add apples and oranges, the answer is a lemon; but if you subtract apples from oranges, the answer can be totally bananas.)

Thank you,
Higurashi

It is an attempt at humor. The words "apples" and "oranges" are often used to describe things that are too different to be compared. The author then included "lemon", which can mean something that doesn't work, and "bananas", which can mean "crazy".