Jar A has 36 litres of mixture of milk and water in the respective ratio of 5 : 4. Jar B which had 20 litres of mixture of milk and water, was emptied into jar A, and as a result in jar A, the respective ratio of milk and water becomes 5: 3. What was the quantity of water in jar B?

Step 1: Analyze Jar A's initial contents

• Total in Jar A = 36 litres
• Ratio of milk to water = 5:4 ⇒ Total parts = 5 + 4 = 9
• Milk in A = (5/9) × 36 = 20 litres
• Water in A = (4/9) × 36 = 16 litres

Step 2: Let milk and water in Jar B be M and W respectively

• M + W = 20 litres (since Jar B contains 20 litres)

Step 3: After pouring Jar B into A, the new total = 36 + 20 = 56 litres

• New ratio = 5 : 3 ⇒ Milk = (5/8) × 56 = 35 litres
• Water = (3/8) × 56 = 21 litres

Step 4: Set up equations using values from both jars

• Milk in A = 20 ⇒ Milk in B = 35 - 20 = 15 litres
• So, M = 15
• Then W = 20 - 15 = 5 litres

Answer: 5 litres

The quantity of water in Jar B was 5 litres.

This is a classic mixture problem involving the addition of two different mixtures and analyzing the resulting ratio. It tests your ability to apply ratio logic and algebra together — a common theme in competitive exams and interviews.