## December 8, 2009

### Homework #40 Answer

During exam periods, cookie sales in the school cafeteria are high. Cookies are selling well in the cafeteria today, so it must be exam time.

Which one of the following is logically most similar to the argument above?

A. Logical thinking is enough to ensure success in the computer programming field. But none of my friends are computer programmers, so they must all be illogical.

(A) is incorrect because it does not match the pattern of the logic in the stimulus. The pattern of the logic in the stimulus is as follows: When the first condition (X) is true, then the second condition (Y) is true; since Y is true, X must also be true. This is not exactly sound logic; in fact, we've seen something like this before in Homework #23 (Answer). Although this is not strictly a cause-and-effect relationship, it is still an attempt to reverse the logic whose result is not always necessarily true. The fact that Y happens whenever X happens does not mean that any time Y happens, X must also have happened.

The logic in choice (A) is flawed, but not for the same reason. The pattern here is that if X is true, then Y is true; since Y is false, X must be false.

B. Someone who thinks logically can become a computer programmer. David thinks very logically, so he can become an excellent computer programmer.

(B) is incorrect because there is no flaw in the logic here. This is a simple attempt to state a general rule and then cite a specific example that follows the rule. If X = Y, and David = X, then David = Y.

C. Skill in thinking logically is one guarantee of success at computer programming; a degree from a prestigious technical school like M.I.T. is another.

(C) is incorrect because there is really no logical sequence in this statement at all. This is a simple statement of fact. X = Z and Y also = Z. Nothing wrong with that, and it certainly doesn't match the stimulus.

D. A computer programmer must be able to think logically. Rob is a very logical person, so he must be a computer programmer.

(D) is correct. Like the stimulus, this tells us that when X is true, Y is true; since Y is true, X must also be true. This choice exhibits the same logical flaw as the stimulus.

E. Computer programmers are always able to solve logic problems. None of the students can solve logic problems, so none of them are computer programmers.

(E) is incorrect because it's perfectly logical. If X can always do Y, and none of the students can do Y, then none of the students can be X.