1. Can I ask you to wash the dishes?

2. May I ask you to wash the dishes?
3. Might I ask you to wash the dishes?
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What is the difference between #1 and #2? Do you use #3?

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4. Where can I find the post office?
5. Where is the post office?
6. I'm looking for the post office.
7. How can I get to the the post office?
8. Can you show me how to get to the post office?
9. How can I go to the post office?
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Q1: Are the questions all grammatical? Do you use them frequently?
Q2: What about #9? Can we use 'go to' instead of 'get to'?

Technically, the word "can" is asking if you are able -- that is, are you physically able to do the task. (This phrasing is often used as an alternate to "may...")

The words "may" and "might" are asking permission. #3 is not often used.

#s 4-8 are all correct and used often. #9 makes sense, but seems a bit odd.

1. Can I ask you to wash the dishes?

To answer this question, the phrase "Can I ask you to wash the dishes?" is grammatically correct. In this sentence, the speaker is asking for permission to make a request.

2. May I ask you to wash the dishes?
Similar to the first question, this sentence "May I ask you to wash the dishes?" is also grammatically correct. It is a more polite way of asking for permission to make the request.

3. Might I ask you to wash the dishes?
This sentence "Might I ask you to wash the dishes?" is also grammatically correct. It is another way of asking for permission to make the request, but it sounds a bit more formal and less commonly used in everyday speech.

Regarding the difference between #1 and #2, both are equally grammatically correct and can be used interchangeably. The only difference lies in their level of politeness. "May I ask you" is generally considered more polite than "Can I ask you."

As for #3, while it is grammatically correct, it is not commonly used in everyday speech. It is more formal and may sound outdated in certain contexts.

Moving on to the second set of questions:

4. Where can I find the post office?
5. Where is the post office?
6. I'm looking for the post office.
7. How can I get to the post office?
8. Can you show me how to get to the post office?
9. How can I go to the post office?

Q1: Are the questions all grammatical? Do you use them frequently?
All the questions in this set are grammatically correct. Regarding frequency of use, it depends on the situation and the individual's needs. For example, if you are in a new area and need directions, questions like #4, #5, #7, and #8 would be more commonly used. #6 and #9 can also be used to express that you are searching for the location of the post office.

Q2: What about #9? Can we use 'go to' instead of 'get to'?
Yes, you can use "How can I go to the post office?" instead of "How can I get to the post office?" Both versions are grammatically correct and convey the same meaning. The choice between "go to" and "get to" depends on personal preference and the context in which you are asking the question.