Question

How many liters of water containing 7 grams of salt per liter must be combined with x liters of water which contains y grams [y is less than 2] of salt per liter to yield a solution with 2 grams of salt per liter.

Answer 1

`((2-y)x)/(5)\text{ litres}`

Explanation:

Let l litre of 7 grams of salt per litre is combined with x litres of water which contains y grams of salt per litre to yield a solution with 2 grams of salt per litre.

Thus,

Salt in l litre + salt in x litre = salt in resultant mixture

7l + xy = 2(l +x)

7l + xy = 2l + 2x

7l - 2l = 2x - xy

5l = x(2-y)

`\implies l =(x(2-y))/(5)`

Hence,
`(x(2-y))/(5)` litres of 7 gram of salt per litre is mixed.