问题
单项选择题
If a three-digit number is selected at random from the integers 100 to 999, inclusive, what is the probability that the first digit and the last digit of the integer will both be exactly two less than the middle digit ？（）
A. 1:900
B. 7:900
C. 9:1,000
D. 1:100
E. 7:100
答案
参考答案：B
解析：
There are exactly 7 digits out of the 900 for which this statement is true: 131, 242, 353, 464, 575, 686, 797; that equals a probability of 7 out of 900.