SAT官方数学习题

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

　　Troy bought a bag of 20 marbles for $2.00, a bag of 50 marbles for $4.00, and a bag of 100 marbles. If the average (arithmetic mean) cost of the marbles in all three bags was exactly $0.08 each, what was the price of the bag of 100 marbles?

　　A. $7.00

　　B. $7.20

　　C. $7.40

　　D. $7.60

　　E. $7.80

　　Correct Answer: D

　　Here‘s Why:

　　If the average price of all 20 + 50 + 100 = 170 marbles was exactly $0.08 each, then the total price of all the marbles was (170)(.08) = 13.60 dollars. Therefore, the price of the 100-marble bag was 13.60 – 2.00 – 4.00 = 7.60 dollars.

　　Difficulty: Medium

　　Question Type: Standard Multiple Choice