SAT官方每日一题 2017年3月29日.

SAT试题类型:Mathematics > Standard Multiple Choice Please enter an answer. Read the following SAT test question and then click on a button to select your answer. If half the people in a room leave at the end of every five-minute interval and at the end of twenty minutes the next to last person leaves, how many people were in the room to start with? (Assume that no one enters the room once the process begins.) Answer Choices (A) 32 (B) 28 (C) 16 (D) 12 (E) 8 答案:C 解析: Explanation At the end of each five-minute interval, half the number of people in the room leave and the other half remain. At the end of twenty minutes, this step of half leaving and half remaining involved only 2 people, 1 leaving and 1 remaining. This means that during the preceding five-minute interval (the interval from minute 15 to minute 20), there were 2 people in the room. At the end of minute 15, the step of half leaving and half remaining must have involved 4 people, 2 who lt and 2 who remained. By the same reasoning, at the end of minute 10 the step involved 8 people, and at the end of minute 5 it involved 16 people. These 16 people were the ones who were in the room to start with, so the correct answer is 16.