Given:
The bottles have equal capacity
Ratio of milk to water = 5 :7, 7:9, and 2 : 1 respectively
Calculation:
Let the capacity of each bottle be y
For bottle 1, milk be 5a and water be 7a
⇒ 5a + 7a = y
⇒ a = y/12 …(i)
For bottle 2, milk be 7b and water be 9b
⇒ 7b + 9b = y
⇒ b = y/16 …(ii)
For bottle 3, milk be 2c and water be c
⇒ 2c + c = y
⇒ c = y/3 …(iii)
⇒ Percentage of milk can be given as = (5a + 7b + 2c) × 100/(5a + 7b + 2c + 7a + 9b + c)
⇒ Percentage of milk = (5a + 7b + 2c) × 100/(12a + 16b + 3c) …from (i), (ii) and (iii)
⇒ Percentage of milk = (5 × y/12 + 7 × y/16 + 2 × y/3) × 100/(y + y + y)
⇒ Percentage of milk = 50.7%
∴ the percentage of milk be 50.7%
Alternate Method
Calculation:
Let quantity of milk and water in bottle-1 = 5 + 7 = 12 units
Quantity of milk and water in bottle-2 = 7 + 9 = 16 units
And the quantity of milk and water in bottle-3 = 2 + 1 = 3 units
As we have an equal quantity of mixture in all bottles
Making the quantity in all bottles equal by making total quantity = 48 liters
For bottle-1
Milk : water = (5 : 7) × 4 = 20 : 28, total 48 liters
For bottle-2
Milk : water = (7 : 9) × 3 = 21 : 27, total 48 liters
Fore bottle-3
Milk : water = (2 : 1) × 16 = 32 : 16, total 48 liters
Total quantity of mixture = 48 × 3 = 144 liters
Total quantity of milk = 20 + 21 + 32 = 73 liters
Percentage of milk = 73/144 × 100
⇒ 0.5069 × 100 = 50.69 or 50.7 %
Hence, the percentage of milk in new mixture is 50.7