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Well at 50% it is probably (I guess around 50% chance this is right), as close to guessing with the 3 options just basing it upon what the weather is like. Raining likely to be small, so predict small, but could end up falling into the medium, unlikely to be large. It's hot and dry, likely to be large, predict large but but could fall into medium, unlikely to fall into small. Based on that you have a little under 50% change of being correct, all depending upon the types of fires and weather they used to train and test against. But they did say it was simple.