①To make your life easier, convert percentage to fractions first.
80% = 80/100 = 4/5
50% = 50/100 = 1/2
②From the fractions we can come up with the ratios :
Tea : Coffee = 4 : 5
Soft Drinks : Tea = 1 : 2
Now , tea is the repeated identity. So change the ratio to the same number for the tea.
Soft Drinks : Tea = 1 : 2 = 2 : 4
The combined ratio can then be written :
Soft Drinks : Tea : Coffee : Total = 2 : 4 : 5
③Total = (2 + 4 + 5) units = 11 units
11 units = 660 cups
1 unit = 660 cups ÷ 11 = 60 cups
Total number of cups of coffee and tea = 9 units (because 4 + 5) = 9 × 60 cups = 540 cups
20% = 20/100 = 1/5
Total number of cups of soft drink = 2 units = 2 × 60 = 120
So 1/5 of total number of cups of tea and coffee = 540 × 1/5 = 108 (or 540 ÷ 5 = 108)
Number of cups of soft drink that needs to be sold = 120 - 108 = 12