There is a proportional relationship between any length measured in centimeters and the same length measured in millimeters. There are two ways of thinking about this proportional relationship. If you know the length of something in centimeters, you can calculate it’s length in millimeters

Each person in an it department of 25 people works on at least one of 3 major projects: system security, program implementation, platform development. 10 people work on system security, 13 work on program implementation, and 12 work on platform development. 4 people work on system security and platform development, 5 people work on program implementation and platform development, and 2 people work on all three projects. how many people work on system security and program implementation?