Not necessarily. The sum of two Irrational Numbers can be rational or irrational.
Yes, you can.
Yes. The sum of two irrational numbers can be rational, or irrational.
Sure; for example, 10 + pi is irrational, 10 - pi is irrational. Both are positive. If you add them, you get 20.
No, you can't.
yes * * * * * No. Rational and irrational numbers are two DISJOINT subsets of the real numbers. That is, no rational number is irrational and no irrational is rational.