If you give, you will receive twice as much.
I think most English speakers would understand what you mean if you said it this way. I might phrase it as :
What you give, you will receive twofold.
to make the tone more like a proverb.
I feel like there's a similar idiom in English but I can't recall the exact wording. The only thing that springs to mind is the quote from Shakespeare's The Merchant of Venice about the quality of mercy:
it is twice blest;
It blesseth him that gives and him that takes:
[No 2. are both bad grammar. Do not use either of these.]
Persuasion can only be done before someone has decided.
"Why don't you take that class?"
This is often used to encourage someone to do something. It is more polite than telling them to do something.
They will respond as if it was a suggestion: "That's a good idea".
Questioning can only be done after someone has decided.
So they can respond as if it was a question.
To make it clearer that it is a question you can ask
"Why don't you want to take that class?" or "Why can't you take that class?"
If it is possible to change their minds then it is both a question and persuasion. If they don't like their decisions being questioned they will respond "Because I don't want to".
If it is too late then it can not possibly be a persuasion. It has to be a question by elimination.
When a question is equivalent to an imperative it is just as rude. Do not ask "Why don't you go to hell?" https://www.youtube.com/watch?v=jOflpNvy_30&t=0m23s
Best Answer
This sentence alludes to a common device for announcing a surprising event, “I’ll give you three guesses wh— ...”:
The three guesses device (which is in origin a storytelling device for building suspense†) suggests that the event is so improbable that even with three successively more far-fetched tries you will not succeed in guessing the right answer.
By contrast, “I'll give you one guess” suggests that the answer is so obvious you only need one guess to get it right. A common variant is
† For instance: