For a standard double six set domino and starting with a double six,
6|6 followed by 6|5 followed by 5|5 followed by 5|4 followed by 4|4 followed b 4|4 followed by 4|3 followed by 3|3 followed by 3|2 followed by 2|2 followed by 2|1 followed by 1|1 followed by 1|0 followed by 0|0
The last number is 0
100%/x%=80/20
(100/x)*x=(80/20)*x - we multiply both sides of the equation by x
100=4*x - we divide both sides of the equation by (4) to get x
100/4=x
25=x
x=25
It adds up to 180 degrees
