This question is similar to this one, but it does not help me, so I am asking it by myself.
I want to know which one is appropriate:
The number of coins in bottle A and bottle B is compared.
The numbers of coins in bottle A and bottle B are compared.
Here what I want to say is "The number of coins in bottle A and the number of coins in bottle B are compared."
I want to know the general rule for this kind of situations (this specific example is not important). In case, the example is strange, I give another one.
The weight of bottle A and bottle B is compared.
The weights bottle A and bottle B are compared.
Best Answer
You should use the plural.
Let's look at it without the center section:
For me, the answer is obvious. You can't compare a single thing with itself without getting equivalence. The plural is required here. So, when we add more information, the plural should be retained:
And this, too makes more sense than the singular. With the singular, I end up asking "to what???"... The number of coins is compared... to what?
So, again, the plural is correct. There are two weights and two numbers.
I also note that you don't have to repeat the nouns:
And I'd say that here, the plural is better sounding, now that you obviously have bottles - plural.
When you use the singular, I'm prepared for a single number/weight, so the second half of the sentence becomes confusing.