Correct Answer - Option 3 : 100 liters

**Given**

A mixture of 100 liters of salt and water contains 20% salt

Water becomes 90% of the new mixture

**Concept used **

Mixture and allegation concept used

**Calculation**

Quantity of salt in the mixture initially be 100 × 20/100 = 20 liters

⇒ Quantity of water = 100 - 20 = 80 liters

⇒ New mixture = 1 : 9

⇒ Let the water be added x liter to make 90%

⇒ 20/(80 + x) = 1/9

⇒ 80 + x = 180

⇒ x = 100

**∴ 100 litre more water should be added **