In what ratio should milk costing Tk 40 per litre be mixed with milk costing Tk 60 per litre to get a mixture worth Tk 50 per litre?

Question: In what ratio should milk costing Tk 40 per litre be mixed with milk costing Tk 60 per litre to get a mixture worth Tk 50 per litre?

Solution:
Use the allegation method:
Cheaper = 40, Costlier = 60, Mean = 50
=> Ratio = (60 – 50):(50 – 40) = 10:10 = 1:1

Alternative:
Let Tk 40 per liter is consists of x liters,
Tk 60 per liter is conists of y liters.
total milk = (x+y) liters
and price of mixture is 50 tk per liter

Now,
→ 40x + 60y = 50(x + y)
→ 40x + 60y = 50x + 50y
→ 10y = 10x
→ x : y = 1 : 1