Question 159
Prove that if $a, b, c, d \in [1, 2]$, then
$$
\frac{a+b}{b+c} + \frac{c+d}{d+a} \le 4 \cdot \frac{a+c}{b+d}.
$$
$$
\frac{a+b}{b+c} + \frac{c+d}{d+a} \le 4 \cdot \frac{a+c}{b+d}.
$$
MathNet 2017-part-04 — 176 problems (EN–VI) Question 159
Math Olympiad Vault · MathNet 2017-part-04 — 176 problems (EN–VI)