People on bikes must wear a helmet.

[felicity.zyy]

Hi!
People on bikes must wear a helmet. Why isn't this sentence "People on bikes must wear helmets"? I mean, the front part of the sentence is in the plural. Shouldn't we use the plural form in the latter part either?

 

[bennymix]

There are four possibilities for 'bike' and 'helmet'. Aside from both singular, this is not bad, in my opinion. "people ... wear helmets"-- double plural-- somehow reminds me of two heads.

 

[felicity.zyy]

There are four possibilities for 'bike' and 'helmet'. Aside from both singular, this is not bad, in my opinion. "people ... wear helmets"-- double plural-- somehow reminds me of two heads.

Thank you. If a mother has three children and she gives every child a present.(everyone has only a present) In this situation, should I say " The children are given a present" or "The children are given presents"?

 

[bennymix]

Thank you. If a mother has three children and she gives every child a present.(everyone has only a present) In this situation, should I say [1]" The children are given a present" or [2]"The children are given presents"?

Yes, 1 might meam one present for all, BUT 2 does not say how many presents per child. If you mean 'one per', I'd suggest,
[3]"The children are each given a present." or [4]"Each (and every) child gets a present" though in fact 4 does not exclude a child, or several, getting more than one.