Question

in a standard casino dice game the roller wins on the first roll if he rolls a sum of 7 or 11. what is the probability of winning on the first roll?

Answer 1

Answer-

The probability of winning on the first roll is 0.22

Solution-

As in the game of casino, two dice are rolled simultaneously.

So the sample space would be,

$|S|=6^2=36$

Let E be the event such that the sum of two numbers are 7, so

E = {(1,6), (2,5), (3,4), (4,3), (5,2), (6,1)}

$|E|=56$

$\therefore P(E)=\dfrac{|E|}{|S|}=\dfrac{6}{36}$

Let F be the event such that the sum of two numbers are 11, so

F = {(6,5), (5,6)}

$|F|=2$

$\therefore P(F)=\dfrac{|F|}{|S|}=\dfrac{2}{36}$

Now,

$P(\text{sum is 7 or 11)}=P(E\ \cup\ F)=P(E)+P(F)=\dfrac{6}{36}+\dfrac{2}{36}=\dfrac{8}{36}=\dfrac{2}{9}=0.22$