The number of milligrams of a certain medicine a veterinarian gives to a dog varies directly with the weight of the dog. If the veterinarian gives a 30 -pound dog 3 fifths milligram of the medicine, which equation relates the weight, w , and the dosage, d ?

Because dosage varies directly with weight, write d = kw, where k is the dosage per pound. For a 30-pound dog receiving 3/5 milligram, k = (3/5) ÷ 30 = 1/50. Therefore, the equation is d = (1/50)w, which is choice B.

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