How many quarts of pure antifreeze must be added to 9 quarts of a 10% antifreeze solution to obtain a 30% antifreeze solution?

2.6 quarts

Explanation:

According to ratio and proportion:

where,

= concentration of first solution = 10 %

= mass of first solution = 9 quarts

= concentration of pure solution = 100%

= mass of pure solution = x quarts

= concentration of final solution = 30 %

= mass of final solution = (9+x) quarts

Thus 2.6 quarts must be added to 9 quarts of a 10% antifreeze solution to obtain a 30% antifreeze solution.

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