SAT数学题求解Theintegers1through6appearonthesixfacesofacube,oneoneachface.Ifthreesuchcubesarerolled,whatistheprobabilitythatthesumofthenumbersonthetopfacesis17or18?答案是1/54,求思考过程和详细

Question

SAT数学题求解
The integers 1 through 6 appear on the six faces of a cube, one on each face. If three such cubes are rolled , what is the probability that the sum of the numbers on the top faces is 17 or 18? 答案是1/54,求思考过程和详细解释

Answer 1

三次的和为18只有一种情况,6+6+6=18
三次的和为17的有如下几种情况
6+6+5=17
6+5+6=17
5+6+6=17
所以一共是4种情况下可以得到17或者18
扔一次有6种情况,扔3次的话就是6*6*6=216种情况
所以满足条件的概率就是4÷216=1/54