On a 200 question multiple choice test, Mr. Brown took 50 questions and noticed 13 had the answer A, 12 had the answer B, 16 had the answer C, and 9 had the answer D. Using the probability from this experiment, how many questions should have the answer D in the entire test? 36

33

34

35

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.