# The choice between the plural and the singular in complex concept

Thank you for being interested in my question.

Here is an example. Person A three apples, and Person B has four apples. Now I want to discuss these seven apples. Which of these should I say:

Please see our paper for the details of the two persons’ apple.
Please see our paper for the details of the two persons’ apples.

Here is another example.

Nation A invaded nation B, and Nation B invaded nation A, too. So the situation is the two nations invaded each other. Which should I say:

The two nations invaded each other’s territories.
The two nations invaded each other’s territory.

And here comes a third example. Suppose there are 50 people in my class. Each of them has an iPad. Which is the way to combine the above two sentences into one? (I don't think the first choice below is right.)

The 50 people in my class have an iPad.
The 50 people in my class have an iPad each.
Each of the 50 people in my class has an iPad.

What if the situation is that each of them has two iPads? Which can I say:

The 50 people in my class have two iPads each.
Each of the 50 people in my class has two iPads.

"Please see our paper for the details of the two persons' apples" is correct to my ear. The other example implies they share one apple.

"The two nations invaded each other's territory" is correct to my ear. It's a reciprocal relationship each one invaded the other one.

"The 50 people in my class have an iPad" doesn't say what you want, it implies to me that they share one iPad. The two sentences using "each" both appear correct to me.

Finally, "The 50 people in my class have two iPads each" and "Each of the 50 people in my class has two iPads" both appear correct to me.

“Please see our paper for the details of the two persons’ apples” is correct, as you've used the plural possessive correctly.

“The two nations invaded each other’s territory” is correct, because "each other" is singular.

“Each of the 50 people in my class has an iPad” is correct because "each" is singular.

“The 50 people in my class have two iPads each” and “Each of the 50 people in my class has two iPads” are both correct because "50 people" is plural and "Each" is singular.

Good job!