How many gallons of fuel costing $1.15 a gallon must be mixed with a fuel costing $0.85 per gallon to get 40 gallons of a fuel that costs $1 per gallon? Formulate an equation and then solve it in order to determine how
many gallons of fuel costing $1.15.

What is the difference between regular convex and concave polygons

The two square pyramids are similar. find the total volume of both pyramids if the ratio of their surface areas is 9/16

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?