Directions: Underline the prepositional phrase in each sentence below

9. For a fraction of the cost you can buy a watermelon.-underline for a fraction
10. The boy tried to finish the race at any cost-underline at any cost.
11. At noon we all went to lunch. -underline at noon
12. He is in jeopardy of not graduating. -underline in jeopardy

Can you please be so kind as to check the above answers.

You are correct on 12.

In 9, "you" is the subject of the sentence. "can buy" is the verb. They are not prepositional phrases.
"a watermelon" is the direct object of "can buy", not a prepositional phrase.

In 10, "to" is a preposition, as is "at".

In 11, same words.

9. Underline For a fraction and underline you can buy a watermelon? Would this be correct?

10. Underline tried to finish and underline at any cost. Is this correct?
11. Underline at noon and then underline we all went to lunch.
12.Underline in jeopardy and then of not graduating

Would the above answers be correct?

writeacher is correct. Read the explanations I posted, then you won't have to guess!

So for number 10 underline to finish and then underline at any cost.

Would that be the correct answer for number 10?

"you can buy a watermelon" is a clause, not a prepositional phrase.

"tried to finish" is a main verb and an infinitive, not a prepositional phrase.

"we all went to lunch" is a clause, not a prepositional phrase.

Each of these has two. You have identified only one in each. Read the sites I posted for you below, at your last question.

Also, please read this:

http://www.chompchomp.com/terms/prepositionalphrase.htm

For number 11, underline to lunch. This is the correct answer because to is the preposition in this sentence. You should underline lunch because it is the noun and a prepositional phrase always ends at a noun.

It seems to me that in #12, "graduating" is a verb so it can't be part of a prepositional phrase. Instead, it would seem that the main verb phrase of the sentence is "is ... graduating" (and "not" is an adverb to this main verb phrase). So that would leave "in jeopardy of" as the only preposition phrase in #12.

It also seems to me that in #11, "lunch" is being used as a verb. We could replace "to lunch" with "to eat" and this becomes clearer. The presence of a verb means that "to lunch" is not a prepositional phrase. If Instead it appears that "went to lunch" is the main verb phrase of the sentence, like "went to eat". Thus, "at noon" is the only prepositional phrase in the sentence.