A correction for your cancer example. Now if you take the 50% of people you guessed to be positive for test, only 4.25% will be true positives, indicating 8.5%

A correction for your cancer example. Now if you take the 50% of people you guessed to be positive for test, only 4.25% will be true positives, indicating 8.5% accuracy rate; if you take the 50% people you guessed to be negative for test, 45.75% will be true negatives, indicating a 91.5% accuracy rate. But your overall accuracy rate is 50%.