Each day, a weather forecaster predicts whether or not it will rain. For 80% of rainy days, she correctly predicts that it will rain. For 90% of non-rainy days, she correctly predicts that it will not rain. Suppose that 10% of days are rainy and 90% are non-rainy.
a. What proportion of the forecasts is correct?
b. Another forecaster always predicts that there will be no rain. What proportion of these forecasts is correct?