It's always easy to do these as a fraction. We want won/total games played.
Games = 8 + 10 or 18 games played.
pct = 10/18
pct = 0.5555555556
Round to 3 decimal places.
pct = 0.556
Multiply pct by 100.
So, 0.556 • 100 = 55.6.
The pct sought is 55.6%.
