Hello. Usually, I don't have trouble with verbs agreeing with their antecedents, but this particular sentence has stumped me. For example, I know it is correct to say "White Pines is one of many state parks that HAVE pools." However, I'm unsure in this particular case..."John has ten students, which (is, are) 2 fewer than what Amy has." Thanks for any help or comments! I want to say the verb should be is, but then I think which refers to students, so it should be are.
Both will work-- are you thinking of the numbers or the quantity? 'It is 10 miles to Yokohama' exemplifies a quantity-- I am considering the amount as a unit; 'there are 10 miles to go before we get there'-- I am thinking of each mile along the way.

In your case, I like 'is' also.
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hmm. The example about White Pines actually makes me think...In a sentence such as "The bush was covered with blueberries, which we ate," would "which" be referring to the berries or the bush? I thought that that/which tended to refer to the word preceding it and not the subject, but am I wrong? I could have been creating so many embarrasing sentences if I'm wrong...
No, you're right-- to avoid ambiguity, the dependent clause should be placed in close proximity to its referrent.

If you ate the bush, you would write 'The bush, which we ate, was covered with blueberries'.