2 numbers are 10 units from 0. If you start from zero and count 10 units to the right, you should be at a positive number. But, you can also move 10 units to the left. If you do this, you should be at a negative number that is ALSO 10 units away from 0, just in a different direction than positive number. both are 10 units from 0. There always 2 numbers, one 10 units to the right of zero, and one 10 units to the left of zero. Hope this helped! Tell me if I'm wrong or right. :)
Answer:
The short answer is: yes, the answer to "How do you do?" is "How do you do?" It is also acceptable to reply "I'm fine, and you?" and similar variations. However -- and this is important to the etiquette side of things and not so much the language side -- "how do you do?" is actually not a question!