Sandy bought enough powdered juice mix to make 7 1/2 gallons of juice. if her kids go through 1 1/4 gallons of juice per week, how many weeks of juice did she buy?

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?