Question 40
Among numbers $a+b$, $a-b$, $a b$, $\frac{a}{b}$ exactly two are positive and exactly two are negative. Find the sign of $b$.
MathNet 2019-part-06 — 184 problems (EN–VI) Question 40
Math Olympiad Vault · MathNet 2019-part-06 — 184 problems (EN–VI)