If the correlation coefficient of the data set is -1, how confident can you be that the predicted value will be reasonably close to the actual value?

If the correlation coefficient of a data set is -1, it indicates a perfect negative linear relationship between the variables. In such cases, you can have a high level of confidence that the predicted value will be reasonably close to the actual value. This is because the variables have a strong, inverse relationship, and as one variable increases, the other decreases in a very predictable manner. Therefore, you can make accurate predictions based on this strong negative correlation.