Making mistakes more costlier than others• Giving a loan out to an applicant who is likely to default can be an expensive mistake.• One solution to reduce the number of false negatives may be to reject a larger number of borderline applicants, under the assumption that the interest the bank would earn from a risky loan is far outweighed by the massive loss it would incur if the money is not paid back at all.• The C5.0 algorithm allows us to assign a penalty to different types of errors, in order to discourage a tree from making more costly mistakes.• The penalties are designated in a cost matrix, which specifies how much costlier each error is, relative to any other prediction.