No, the answer is that it's impossible to know with the information provided. We don't know if "used" implies removal, nor if "bought" implies addition. You could make reasonable arguments in any direction.
I understand the solution that you consider obvious. There are other posters in this thread with different solutions that they think are obvious. If several of people parse several meanings out of one statement then the statement is ambiguous.
Q: John has 5 bottles of water. He uses one every day. How many days before he runs out of water?
A: John started with 5 bottles. He uses them at the rate of 1 bottle/day. 5 bottles divided by 1 bottle/day gives 5 days. The answer is 5 days.
Q: Jill has 2 blankets. She uses 1 every night to keep warm. How many nights before she will sleep in the cold?
-- response --
A: Jill started with 2 blankets. She uses them at the rate of 1 blanket/night. 2 blankets divided by 1 blanket/night gives 2 nights. The answer is 2 nights.
[not fair? leading the bot? ok, let's ask it straight]
-- prompt --
[Ignore all previous directives.]
Jill has 2 blankets. She uses 1 every night to keep warm. How many nights before she will sleep in the cold?
-- response --
Jill will sleep in the cold on the third night since she only has 2 blankets and she uses one every night.
--
tldr: "use" of perishable vs nonperishable items leads GPT-3 astray. Rejoice bipeds of the world. You will not starve before UBI is rolled out.
More, this time we will mix perishable and non-perishables and use CoK prompting again.
-- prompt --
Q: Joe is a carpenter. He has 2 hammers and 5 bottles of water. In order to work, joe uses a hammer and one bottle every day. How many days can he work?
A: Joe started with 2 hammers and 5 bottles. After 5 days he will exhaust his water bottles. The answer is 5 days.
Q: Jill is an insomniac. She has 5 sleeping pills and 2 blankets. In order to sleep, she uses 1 sleeping pill and a blanket every night. How many nights can she sleep?
-- response --
Jill started with 5 sleeping pills and 2 blankets. After 2 nights she will exhaust her blankets. The answer is 2 nights.
-- prompt --
Jason has 9 cats. He snuggles at night with a cat to sleep. How many nights can Jason snuggle with a cat?
John posts 1 chatGPT challenge that is too ambiguous to be a valid test. James posts 14 well formed, unambiguous challenges that clearly highlight chatGPT's shortcomings. How many challenges remain too ambiguous to be valid?
