If C < 4 , WHAT ARE THE POSSIBLE VALUES OF D?

[rockrock]

This is from the EIV Flashcards, #17.

If c < 4, what is the range of possible values for d if 3c = -6d.

I tried to solve by isolating d: d = - 1/2 C

Then plugging in numbers for c:
C = then D =
3 -3/2
2 -1
1 -1/2.

Clearly this was wrong because it was an extreme value question where I was supposed to plug in "LT4) in the equation.

My question is how does one easily identify Extreme value questions? What wording should you look for and what flags might there be to tell you you're doing it wrong and SHOULD be using extreme value strategy?

[tim]

There is never a time when you are *supposed* to use extreme values, but instead you should use them if you feel they will help. in general you should also not plug in values as you did in order to find a complete range. If you have a few possible ranges, you can plug in numbers to check which ones work, but for this one your best bet would have been to solve for c, then plug the -2d into the inequality, then solve for d..