How do you know that 8 over 10 and 48 over 60 are equivalent

Find the value of x for which abcd must be a parallelogram -9-6x x-30

The pyramid below was dissected by a horizontal plane which shape describes the pyramid horizontal cross section

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?