单选题 Directions: Questions 8-20 have three different formats. Unless a question has its own directions that specifically state otherwise, each question has five answer choices, exactly one of which is correct.
单选题 In the figure below, what is the average (arithmetic mean) of the measures of the five angles?
【正确答案】 D
【答案解析】The markings in the five angles are irrelevant. The sum of the five angles is 360°, and 360 ÷ 5 = 72. **If you solve the equation a + 2a + 3a + 3a + 3a = 360, you get that [*], and so the degree measures of the five angles are 30, 60, 90, 90, and 90. You would then find that the average of those five numbers is 72; but all of that is a waste of time.
单选题 Camille's average on her 6 math tests this marking period is 75. Fortunately for Camille her teacher drops each student's lowest grade, and this raises her average to 85.What was her lowest grade?
  • A. 2O
  • B. 25
  • C. 30
  • D. 40
  • E. 50
【正确答案】 B
【答案解析】On her six tests combined, Camille earned a total of 6 × 75 = 450 points. The total of her five best grades is 5 × 85 = 425 points, so her lowest grade was 450 - 425 = 25. **Assume that Camille's five best grades were each 85. Then each one has a deviation of 10 points above the average of 75, and the total deviation above 75 is 5 × 10 = 50 points. Therefore, her one bad grade must have been 50 points below 75.