Great questions! 1. Yes, the question that makes the most logical and grammatical sense is "why are you asking". However, for some reason, this is seen as an aggressive way to ask the question. A: "Do you have the money?" B: "Why are you asking?" [B glances significantly at his gun]. It is much more polite to say "Why do you ask?" This makes it sound more abstract and theoretical. It is similar to the way that we often use conditional for requests. "Can you come over here?" sounds a bit rude. "Could you come over here?" sounds much more polite. it implies "Could you come over here, [if I were rude enough to ask you to do that]?" B. Neither. You should say "I've forgotten how much I paid." "Forget" is the opposite of "learn", not "know". When something changes from not being in your brain to being in your brain, you learn it. When it is in your brain, you know it. When it changes from being in your brain to not being in your brain, you forget it. After it leaves your brain, you have forgotten it. You never notice the exact moment when something leaves your brain--if you noticed it, you would remember it. Instead, you look at your brain, and see that the information isn't there anymore, so you know that you have forgotten it, but you don't know when you forgot it. SO, for information, always use "forgotten" instead of "forget" or "forgot". When should you use "forget" and ""forgot"? You can use them for actions: --"I forgot to bring my keys" --"Don't forget to bring your keys tomorrow." You can also use them for *temporary* memory failures. --"At the party last night, I forgot Sally's name." [...but you remember it NOW]

"Why do you ask" has a general meaning of, how come you're asking this, how come you wanna know this? It's also a more friendly and idiomatic way of asking someone's intention. "Why are you asking" is not idiomatic and it is more direct and forceful. "I forget" is also a common phrase to say you don't remember at the moment, and "I forgot" is more specific.

"Why do you ask?" is sort of idiomatic. The meaning isn't any different from "Why are you asking?", but it sounds more polite. The question "Why are you asking?" is also fine, in most cases, but it has some potential to sound suspicious or rude, depending on your tone. "I forget" is also somewhat idiomatic, and is interchangeable with "I've forgotten." To me, "I forget how much I paid" sounds much better than "I forgot how much I paid." If you say "I forgot," it sounds like the act of forgetting is something that happened once, and was completed, at a certain point in the past. If the act of forgetting is relevant to the present, we usually indicate that with the tense. For example: "After I stopped using the program, I forgot the password" (past event) "I can't open the program because I've forgotten the password" (present event) I don't know if it's actually grammatically incorrect to say "I forgot" in these cases, but "I forget" or "I've forgotten" both sound much more natural.

grammatically "I forgot how much I paid" "I have forgotten how much I paid" is what you should say in this context and scenario.. "I forget" would = you have memory problems or you are actually in the process of forgetting. This is common to use and very few people question it.. But remember for the class room "to forget" = the act of not remembering, or to describe your condition or tendency to forget..I have forgotten = the actual past act of forgetting anything or something.. Even I sometimes say "I forget" because I hear it all the time, but usually I correct myself by rephrasing with "I have forgotten".. There have been instances of people responding to "I forget" with "you need to see a doctor" or other witty remarks to point out the subtle differences in some situations.

The natural way to challenge the right to ask the question, is to respond with: Why do you need to know that? Overkill, on favourite restaurant, then may be "Is there a particular reason you're asking that?" Obviously a woman might think you've romantic intentions. Seems to me the suggested alternative answers fail to address the situation. Asked naïve questions, I'm not going to answer I'd likely make something silly up ... then change to yet sillier answer if the question is repeated.