SAT官方每日一题 2017年7月3日.

SAT试题类型 Mathematics > Standard Multiple Choice Read the following SAT test question and then click on a button to select your answer. A 6-sided number cube, with faces numbered 1 through 6, is to be rolled twice. What is the probability that the number that comes up on the first roll will be less than the number that comes up on the second roll? (A) 1 over 4 (B) 1 over 3 (C) 5 over 12 (D) 7 over 12 (E) 1 over 2 答案:C 解析

The outcome space for this experiment is the set of all ordered pairs where represents the first number that comes up, and represents the second one. Since and can take all the values through , there will be a total of possible outcomes. The outcomes can be represented in a table as shown:

Among all the pairs, are pairs for which . So remaining pairs will have . Notice that the number of pairs for which is the same with the number of pairs

for which . Therore the number of pairs

for which , is (half of ). Then the probability that is equal to . 相关阅读 SAT官方每日一题 2011年7月6日 SAT官方每日一题 2011年7月5日 SAT官方每日一题 2011年7月4日 SAT官方每日一题 2011年7月3日 SAT官方每日一题 2011年7月2日 SAT官方每日一题 2011年7月1日