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Mathematics>Standard Multiple Choice

Read the following SAT test question and then click on a button to select your answer.

Milk costs x cents per half-gallon and y cents per gallon. If a gallon of milk costs z cents less than 2 half-gallons, which of the following equations must be true?

(A) x-(2*y)+z=0
(B) (2*x)-y+z=0
(C) x-y-z=0
(D) (2*x)-y-z=0
(E) x+(2*y)-z=0

答案和解析

答案：D

解析：

The cost of a gallon of milk (y cents) is equal to z cents less than the cost of 2 half-gallons ((2*x) cents). This can be written algebraically as y = (2*x)-z. Subtracting y from both sides of the equation yields (2*x)-y-z = 0.