The ratio of red to blue to yellow balloons is 5 : 3 : 9. Yellow balloons are 9 units and equal 54.<br><br>[[model:questions/solutions/q4501.png]]<br><br>• Yellow → 9 units = 54 balloons<br>• $$\frac{1}{1}$$ unit → 54 ÷ 9 = 6<br>• Red → 5 units → 5 × 6 = 30<br><br>There are 30 red balloons.<br>Check: Blue = 3 × 6 = 18. Ratio check: 30 : 18 : 54 = 5 : 3 : 9. ✓