请问一道SAT数学题A 6-sided number cube,with faces number 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 comes up on the second roll?

Question

请问一道SAT数学题
A 6-sided number cube,with faces number 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 comes up on the second roll?

Answer 1

这题和OG的P408-5是一样的题目.
扔2次,所得结果就有36种,其中两次一样的6种,所以不同的有30种
其中30种里,第一次比第二次大的种类和第一次比第二次小的种类相同,所以题目所求的有15种
答案为15/36