For instance, the ability to rule out one of four choices on a one-point question where a wrong answer costs a quarter point means that you should guess from the remaining three - the expected point value of this guess is positive. If you can rule out one of four choices and a wrong answer costs half a point, leave it blank.

If you can rule out one of four choices, you'll get the right answer 1/3 of the time, and a wrong answer 2/3 of the time, for an expected value of 1(1/3) - (1/2)(2/3) = 0, so it doesn't matter whether you guess or not.