7.1. Are there such numbers $a$ and $b$ for which all four numbers $a+b, a-b, a \cdot b, a: b$ are different and each of these numbers equals one of the numbers $0,9,3,6, \quad 1,6,3,9$?
Answer: Yes, $a=2.4$ and $b=1.5$.

Comments. The suitable pair is unique. If it is indicated correctly - 7 points.