Question

what is the negation of 'Ten heads were obtained'.

Answer 1

Ten heads were not obtained.

Answer 2

@ momin--> I think the negation should be the following:

Nine or fewer heads were obtained.

Answer 3

I believe you were correct with the first statement. "Nine of fewer heads were obtained" is not a complete negation, because what is 11 heads were obtains? That would still negate the original statement, but isn't included in your second statement. I'd say your first statement was the correct one.