Are 20, 18, 5, 6 in proportion?

The correct answer is No

$20:18$ = $\dfrac{20}{18}$ = $\dfrac{10}{9}$

$5:6$ = $\dfrac{5}{6}$

∴ $20:18$ ≠ $5:6$

Hence 20, 18, 5, 6 are not in proportion.