A spirit and water solution is sold in a market. The cost per liter of the solution is directly proportional to the part (fraction) of spirit (by volume) the solution has. A solution of 1 liter of spirit and 1 liter of water costs 30 cents. How many cents does a solution of 1 liter of spirit and 2 liters of water cost? Pick one.
A) 13  B) 30  C) 50  D) 51  E) 52
Yes, ensure that you understand the relation thoroughly!   Cost per liter = K * Fraction of Spirit   30 cents is the cost of 2 liters of solution (1 part water, 1 part spirit). So cost per liter is 15 cents. Fraction of spirit is 1/2.   15 = K * (1/2)   K = 30   Cost per liter = 30 * (1/3) (1 part spirit, 2 parts water)   Cost for 3 liters = 30 * (1/3) * 3 = 50 cents   B. 30 cents
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A spirit and water solution is sold in a market. The cost per liter of the solution is directly proportional to the part (fraction) of spirit (by volume) the solution has. A solution of 1 liter of spirit and 1 liter of water costs 30 cents. How many cents does a solution of 1 liter of spirit and 2 liters of water cost?