Should I put "the" here?

I know that I should usually use "the" before the superlative expression but should I put "the" for the following cases?

#1. Your answer was (the) most informative.

#2. This method is (the) simplest.

#3. What movie do you like (the) best?

#4. My grandmother seems to be (the) happiest when she is with me.

#5. Jack is (the) tallest.

I've seen some conflicting usages for using proper "the".

Can native speakers of English explain these?

Your answer was THE most informative OF ALL THE ANSWERS.

This method is THE simplest AVAILABLE.

Jack is THE tallest IN HIS CLASS.

I'm currently in Japan teaching English and I have recently discovered how confusing 'THE' can be.
When someone says 'your answer was most informaative', it does not necessarily mean THE most informative. It can just as easily mean that it was very informative. Hope this helps, one of my fellow English teachers who has a higher knowledge of the machanics of English than me often asks me questions like "Why is it THE Eiffel Tower but not THE Big Ben?"