tense question

[vkhu]

Rewrite the sentence:
Mary knew what the answer was after reading the book

This is the key:
->By the time she finished reading the book, Mary knew what the answer was

Something is very weird about it. Isn't it supposed to be Marry had known?

[5jj]

The past perfect form is correct, but not essential.

ps (later): Please ignore this. My words were about the first verb, and vkhu was asking about the second. Sorry.

[vkhu]

The past perfect form is correct, but not essential.

Huh o.0? Can you elaborate?

[5jj]

When the time sequence is clear, native speakers use the past perfect less frequently than some grammar books suggest they do.

[emsr2d2]

As 5jj said, grammar books generally give a good guide but native speakers will mix up tenses when speaking. As another example, your rewrite could also say:

By the time she had finished reading the book, Mary knew what the answer was.

To echo 5jj, "the past perfect is correct, but not essential" in my version too.

[vkhu]

ok, so bottom line is that stuff work well on paper but in practice it's better to go with the past tense. thanks

[5jj]

ok, so bottom line is that stuff works well on paper but in practice it's better to go with the past tense. thanks

No, we didn't say that. emsr2d2 and I both said that the past perfect was correct in the example you gave. I think I would probably use it there.

ps (later): Please ignore this. My words were about the first verb, and vkhu was asking about the second. Sorry.

[Raymott]

Rewrite the sentence:
Mary knew what the answer was after reading the book

This is the key:
->By the time she finished reading the book, Mary knew what the answer was

Something is very weird about it. Isn't it supposed to be Marry had known?

No, it definitely should not be "By the time she finished the book, Mary had known what the answer was." You cannot use the past perfect in this clause.

You could possibly use the past perfect in the other clause (as the answer key has done for some reason), but I can't think why you'd write anything other than, "After reading the book, Mary knew what the answer was" - unless an instruction to rewrite a sentence meant, "Rewrite the sentence making whatever tense changes you like."
(I assume you're not meant to add or delete elements when re-writing).

[5jj]

I apologise for giving confusing answers, I somehow misread the original question and thought you were asking about the first verb. I must read the questions more carefully.

Thanks to Raymott for picking this up.