One -fifth The sum of 1/2 and 1/3

How do you solving the solution of each system using elimination?

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?

How can you find the magnitude of a vector, v = < x,y > , where the horizontal change is x and the vertical change is y?