English
posted by rfvv .
1. He can not solve the math problem.
2. He cannot solve the math problem.
3. He can't solve the math problem.
4. He could not solve the math problem.
5. He couldnot solve the math problem.
6. He couldn't solve the math problem.
(Are they all grammatical? What about #5? Is it wrong expression?)

#5 is definetly wrong Also Im not sure about number 2.

All are correct except #5.