Final-Answer:
The difference in meaning between the two sentences is that in the first sentence, "ten day-old chicks," the word "day" is a noun and refers to the number of days that the chicks have been alive. In the second sentence, "ten-day old chicks," the word "day" is an adjective and modifies the word "chicks," meaning that the chicks are ten days old.
To be more clear:
In the first sentence, "ten day-old chicks," the word "day" is a noun. It is the object of the preposition "of." The prepositional phrase "of ten days" modifies the noun "chicks." This means that the chicks are ten days old.
In the second sentence, "ten-day old chicks," the word "day" is an adjective. It modifies the noun "chicks." This means that the chicks are old enough to have been alive for ten days.
The difference in meaning between the two sentences is subtle, but it can be important in some contexts. For example, if you are buying chicks, you would want to make sure that you are getting chicks that are actually ten days old. If you were to buy "ten day-old chicks," you might not be getting chicks that are actually ten days old.
