Question

When rolling two six-sided number cubes, what is the probability of getting a sum of at least 5? 5/18 1/3 13/18 5/6

Answer 1

The sample space for two six sided cubes =

(1,1) (1,2) (1,3) (1,4) (1,5) (1,6)

(2,1) (2,2) (2,3) (2,4) (2,5) (2,6)

(3,1) (3,2) (3,3) (3,4) (3,5) (3,6)

(4,1) (4,2) (4,3) (4,4) (4,5) (4,6)

(5,1) (5,2) (5,3) (5,4) (5,5) (5,6)

(6,1) (6,2) (6,3) (6,4) (6,5) (6,6)

Now the favourable events are those where the sum is greater than or equal to 5.

It means

(1,4) (1,5) (1,6)

(2,3) (2,4) (2,5) (2,6)

(3,2) (3,3) (3,4) (3,5) (3,6)

(4,1) (4,2) (4,3) (4,4) (4,5) (4,6)

(5,1) (5,2) (5,3) (5,4) (5,5) (5,6)

(6,1) (6,2) (6,3) (6,4) (6,5) (6,6)

It means

favourable events = 30

and total possible events = 36

So probability = 30/36 = 5/6

Hence 4th option is the correct one.