To answer this you need to find the probability that it is 18 first. The only way to get 18 is by rolling 3 6's. The probability of each 6 is 1/6. 1/6 * 1/6 * 1/6= 0.0046. That is the probability of rolling 3 die and getting 18. To get the actual answer, you just subtract that from 1 1-0.0046 equals 0.9954
