<p>Source: Collegeboard 2nd Edition "Bluebook" Test 6, Section 2, Question 19</p>
<p>If a, b, c and f are four non zero numbers, then all of the following proportions are equivalent EXCEPT:</p>
<p>(A): a/f = b/c
(B): f/c = b/a
(C): c/a = f/b
(D): a/c = b/f
(E): af/bc = 1/1</p>
<p>I think this question was a typo, there was no diagram provided and it is impossible to solve.</p>
<p>I remember this question and thinking the exact same thing. Without any specification into the values of a, b, c, and f, I don’t know how to solve it either.</p>
<p>You would cross multiply each expression,</p>
<p>A. Is ac=bf <— Obviously not the same as the other ones. A is the answer.
B. af=bc
C. bc = af
D. af=bc
E. af=bc</p>
<p>I have the answer, from the official college board online sat course. It says that from the fractions, when you cross multiply all of the answer choices except A, they show that af = bc, but in choice A the cross multiplication leads to ac = fb which is not the same.</p>
<p>I hate these kind of questions, it doesn’t test your math skills at all; just deductive thinking.</p>
<p>I hear ya mate, but I took 2 SATs, and those type of questions that require a specific way of thinking show up all the time. (For this question, if you didn’t realize to cross multiply, it would be very difficult to solve.)</p>
<p>@AznSkyDragon</p>
<p>That is what the SAT tests, your ability to use deductive reasoning to solve puzzles. In this section, the puzzles just happen to look like math problems. The question asks you to compare each answer and find which is not equivalent and when faced with a fraction equal to a fraction your first thought should be to cross multiply.</p>