Are these correct? If not, why?
1. You will receive a ten dollar gift card.
2. You will receive a ten dollars gift card. (If this is wrong, why? Isn't 'ten' plural? Like 'You will receive a pair of gift cards." 'Pair' is plural.)
Statement: It's five dollars cheaper.
Question: How much cheaper?
Answer: Five dollars.
'Five dollars' modifies the comparative adjective 'cheaper', and functions as an adverb. It is also a noun phrase in form: adjective 'Five' + noun 'dollars'. (Note that, 'dollars' requires an -s because its modifier 'Five' is plural.)