if you roll two fair six sided dice, what is the probability that the sum is four or higher

Question

please help me i dont understand

Answer 1

The die can give you a sum of 2 - 12.  It's probably easier to figure out what the probability is that the sum is 2 or 3 and then subtract that probability from 1.

 

prob(2) = (1/6)*(1/6) = 1/36  (there's only 1 way to roll a sum of 2: both dice must have been 1's).

prob(3) = 2 * (1/36) = 2/36  (there are 2 ways to get a sum of 3: the first die is a 1 and the second a 2 or vice versa).

 

Therefore, the probability of getting a sum of 2 or 3 is: (1/36) + (2/36) = 3/36 = 1/12

Subtracting that from 1: 1 - (1/12) = 11/12.