1. You will must go hunting. (X)

2. You will have to go hunting. (O)

3. He may can lift the rock.(X)
4. He may be able to lift the rock. (O)

5. She must can solve the math problem. (X)
6. She must be able to solve the math problem. (O)

(Are the marks, X's and O's, used correctly?)

7. She may will go to London tomorrow.

8. She may be going to go to London tomorrow.

9. She will may go to London tomorrow.
10. She will _________ go to London tomorrow.

(Which ones are grammatical? What words can be put in the blank?)

2, 4, 6 and 8 are correct.

10. possibly, probably, likely?

There are two sets of auxiliary verbs (helping verbs) to make a variety of English tenses. The set that 1) helps us make progressives, futures, and possibilities, and the set that 2) helps us make the perfect tenses.

This webpage does a pretty good job of explaining some of them and their uses.
http://grammar.ccc.commnet.edu/grammar/auxiliary.htm

Basically, you can combine some in set one with some in set two, but rarely can you combine those in set one with another from set one.

I hope that makes sense!

In this given set of sentences, the X marks indicate incorrect usage, while the O marks indicate correct usage.

1. You will must go hunting. (X)
Explanation: The correct sentence would be "You will have to go hunting." Use "have to" to express a requirement or obligation.

2. You will have to go hunting. (O)
Explanation: This sentence is grammatically correct and expresses a requirement or obligation to go hunting.

3. He may can lift the rock. (X)
Explanation: The correct sentence would be "He may be able to lift the rock." Use "be able to" to express possibility or capability.

4. He may be able to lift the rock. (O)
Explanation: This sentence is grammatically correct and expresses the possibility or capability of lifting the rock.

5. She must can solve the math problem. (X)
Explanation: The correct sentence would be "She must be able to solve the math problem." Use "must be able to" to imply capability or requirement.

6. She must be able to solve the math problem. (O)
Explanation: This sentence is grammatically correct and expresses the requirement or expectation of being able to solve the math problem.

Now, let's address the remaining statements:

7. She may will go to London tomorrow. (X)
Explanation: This sentence is incorrect. "May" and "will" cannot be used together. A correct alternative could be "She may go to London tomorrow."

8. She may be going to go to London tomorrow. (O)
Explanation: This sentence is grammatically correct and implies the possibility of her going to London tomorrow.

9. She will may go to London tomorrow. (X)
Explanation: This sentence is incorrect. "Will" and "may" cannot be used together. A correct alternative could be "She may go to London tomorrow."

10. She will _________ go to London tomorrow.
Explanation: Here, you can complete the sentence by adding a suitable phrase or verb to express the future action. For example, "She will definitely go to London tomorrow," or "She will possibly go to London tomorrow." The blank can be filled with adverbs like "definitely," "possibly," "probably," etc., or with any other appropriate verb or phrase.