2/28/11

Test 3 Section 5 - #6 (page 527)

It's pretty rare to see "inversely proportional" on the SAT, but it is fair game. Inversely proportional means:

x1y1 = x2y2

Contrast that with the more common proportionality you'll see, which is DIRECT proportionality:


x1/y1 = x2/y2

Basically, what all this means is:
  • If two variables are inversely proportional, one will go up as the other goes down.
  • If two variables are directly proportional, they both go up at the same time.
If x and y are inversely proportional, then so are x2 and y2. And if those two are inversely proportional, taking the inverse of ONE of them will create direct proportionality. So 1/x2 is directly proportional to y2. That's answer choice (E).

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