Question

1. All of a sudden a funny thing happened.

2. All of sudden a funny thing happened.
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Can we omit 'a' before 'sudden'?

3. detour
(Do we stress the first syllable? Can we stress the second syllable?)

4. I have little money.
5. I have less money than Tom.
6. I have the least money of all my classmates.
(Are they all grammatical?)

Answer 1

No, "a" belongs there. 1 is correct; 2 is incorrect.

3 -- stress on the first syllable, not the second

4 - 6 -- Yes, all are grammatically correct.