If you roll two fair six-sided dice, what is the probability that the sum is 555 or lower?

Rolling a two six-sided dice means we would have (6x6) = 36 combinations.

(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)  

It says to find the combinations whose sum is 5 or lesser. Those favorable combinations would be :-

(1,1) (1,2) (1,3) (1,4)  

(2,1) (2,2) (2,3)  

(3,1) (3,2)  

(4,1)  

So we have favorable 10 combinations.

Probability is the ratio of Favorable combinations to Total combinations.

Probability = 10/36 = 5/18

a - base

b - exponent

so,