Adding the two equations
3x + 6y + 3x - 6y = 36+0
6x = 36
x = 6
.
subtracting second equation from first
(3x + 6y ) - (3x-6y) =36 -0
12y = 36
y = 3
.
therefore
x = 6 and y = 3
(6,3)
If the order doesn't matter, then the probability is 37.5%
If it has to be head head tail, then the probability is 12.5%
If the order doesn't matter, the possible outcomes that have two heads and one tail are HHT, HTH, and THH. Since these all have a probability of 12.5% of occuring, the probability of any of them occuring is 37.5%
