In a math class with 23 students, a test was given the same day that an assignment was due. There were 14 students who passed the test and 15 students who completed
the assignment. There were 12 students who passed the test and also completed the
assignment. What is the probability that a student chosen randomly from the class
did not complete the homework?
8/23

So the first thing we do is to multiply the top equation by 3. the reason i want to do this is i notice there will be a 6y on both equations and can possibly add/subtract them. so we get 6y = -3x + 27. adding that and the second equation we get 6x = 27-15 which is 12. divide by 6 and we get 2. ∴ x = 2. substituting 2 into the first equation we get 2y = -2 + 9 which is 7. divide by 2 and we get 7/2. ∴ y = 7/2, x = 2.