Answer to sparking widgets problem
There’s (1 : 9) bad vs. good widgets. Bad vs. good widgets have a (12 : 4) relative likelihood to spark. This simplifies to (1 : 9) x (3 : 1) = (3 : 9) = (1 : 3), then converts to a probability of 1/(1+3) = 1⁄4 = 25%.