An air pump at a gas station dispenses 90 pounds of air for $0.25. Which of the following expressions gives the number of pounds of air dispensed, P, for d dollars?
A. P = d + 90
B. P = d + 360
C. P = 90d
D. P = 360d
Answer:D
An air pump at a gas station dispenses 90 pounds of air for $0.25. Which of the following expressions gives the number of pounds of air dispensed, P, for d dollars?
A. P = d + 90 B. P = d + 360 C. P = 90d D. P = 360d
Explanation: D Whenever there are variables in the question and in the answers, think Plugging In. Let d = 2. For $1 the air pump dispenses 90 × 4 = 360 pounds of air. Therefore, for $2 the air pump will dispense 360 × 2 = 720 pounds of air. Plug in 2 for d in the answer choices to see which answer equals 720. Choice (A) becomes P = 2 + 90 = 92. Eliminate (A). Choice (B) becomes P = 2 + 360 = 362. Eliminate (B). Choice (C) becomes P = 90(2) = 180. Eliminate (C). Choice (D) becomes P = 360(2) = 720. Therefore, the correct answer is (D).