Homework Help: Another SAT I Math question (proportions)

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1. Jan 18, 2009

Elbobo

1. The problem statement, all variables and given/known data
If a, b, c, and f are four nonzero numbers, then all of the following proportions are equivalent EXCEPT

(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)

2. Relevant equations
None

3. The attempt at a solution
The answer is A, but I have absolutely no clue why. This question doesn't even make sense. And no, there's no diagram or any other info, which makes me think that this question was an error...

2. Jan 18, 2009

HallsofIvy

Perhaps it would make more sense if you wrote it in terms of products, by multiplying on both sides by the denominators, rather than fractions.

(A) is equivalent to ac= bf.
(B) is equivalent to af= bc.
(C) is equivalent to bc= af (which, of course, is the same as af= bc).
(D) is equivalent to af= bc.
(E) is equivalent to af= bc.

Now do you see why all except (A) are equivalent?

3. Jan 18, 2009

Dick

(B)-(F) are all equivalent to af=bc. (A) is equivalent to fb=ac.