GRE数学考试真题及解析(12)

　　A box at a yard sale contains 3 different china dinner set, each consisting of 5 plates. A customer will randomly select 2 plates to check for defects. What is the probability that the 2 plates selected will be from the same dinner set?

　　A. 2/7

　　B. 2/5

　　C. 2/3

　　D. 5/6

　　E. 3/2

　　解析

　　答案：A

　　解析：分子的表达方式是从5个盘子中选2个，一共有10种选法，然后有3个不同的set，所以再乘以3，所以分子是30，分母是从15个盘子中选2个，算出来是105，所以最终答案是30/105=2/7。