Writing constraints using variables.

1. Let x1 and x2 be 0 - 1 variables whose values indicate whether projects 1 and 2 are or are not done. Write the constraint that indicates project 2 can be done only if project 1 is done.


2. Let x1 , x2 , and x3 be 0 - 1 variables whose values indicate whether the projects are or are not done. Write the constraint that indicates that at least two of the projects must be done.


3. Let x1 , x2 , x3, x4, x5, & x6 be 0 - 1 variables whose values indicate whether the projects are or are not done. Write a constraint that says either project 5 or 6 must be undertaken but not both.