A milkman sells milk mixed with water at ₹9 per liter and makes a 20% profit. If the cost price of pure milk is ₹10 per liter, what is the ratio of milk to water in the mixture?

A milkman sells milk mixed with water at ₹9 per liter and makes a 20% profit. If the cost price of pure milk is ₹10 per liter, what is the ratio of milk to water in the mixture?
एक दूधवाला पानी मिला हुआ दूध 9 रुपये प्रति लीटर बेचकर 20% लाभ कमाता है। यदि 1 लीटर शुद्ध दूध का क्रय मूल्य 10 रुपये है, तो उक्त मिश्रण में दूध और पानी का अनुपात है ?