Of 755 drivers, 305 use a phone, 685 had no violation and 280 are both. What is the probability of phone use or no violation?

1. The addition rule adds the two totals and removes the shared cell. 2. That gives 305 plus 685 minus 280, which is 710 drivers. 3. Dividing by the grand total gives 710/755. 4. Adding 305 and 685 without the subtraction gives 990/755, a value above one, which no probability may take. _Source: OpenStax Introductory Business Statistics (CC BY 4.0), Ch 3 "Probability Topics", section 3.4 Contingency Tables and Probability Trees_