Sleep is uncountable but hours are countable. This works with other nouns too, where you include units. I.e. How much bread do you need & how many loaves of bread do you need? I would use 'many' for the second response based on this rule, because hours of sleep are countable.

"Many people need up to 10 hours sleep a day, although a few need only five". The whole sentence is not natural and wrong. Forget about countable and uncountable nouns this is confusing you and others in this sentence. you need to reverse the structure to be naturally fluent. First serious error, you start the sentence wrong with ALTHOUGH, but you have not yet given as anything to compare with. ( first statement, followed by ALTHOUGH, SECOND STATEMENT).

Hi everyone, Thank you for answering this question. I took that sentence from a grammar book, the whole paragraph is: For most adults, seven to eight hours a night appears to be the ideal amount of sleep, although a few people may need as little as five hours' of sleep or as many/much as ten hours' sleep each day.

Lower instead of little. More instead of many and much.

Really? Wow, I would have assumed that hours would win & I would have also been happy with as few as five hours and as many as ten hours. That is, I would have accepted both of them either way, whiole suspecting that both should be few, many :)