Question

Tom rolls 2 fair dice and adds the results from each. Work out the probability of getting a total that is a factor of 21.

Answer 1

The probability of getting a total that is a factor of 21 is 0.22

Explanation:

Factor of 21 is = 1, 3, 7, 21

Out of all the factors of 21, we cannot get 21 when the two die are rolled as the maximum sum that can be obtained is 12

The possible combinations are:

(1,2) (1,6)

(2,1) (2,5)

(3,4)

(4,3)

(5,2)

(6,1)

Total outcome = 6 X 6

                      = 36

Number of outcomes that is the factor of 21 is 8

The probability of getting a total that is a factor of 21 is $\frac{8}{36}$

p(21) = 0.22

Therefore, the probability of getting a total that is a factor of 21 is 0.22