Abhirup,

I'm not sure what version of the Formula Study Guide from

www.pmformulas.com
you are looking at, but in the current version, the question is as follows:

Question 10: PV = 100, EV = 105, BAC = 400, AC = 102, CV = 3. What is the Estimate to Complete (ETC) assuming that work will continue at the planned rate?

Therefore, the question clearly states that the "work will continue at the planned rate" [= the variance will not happen again]. As such the formula used, answer and explanation are correct.

Also consider looking at this from the perspective of the available answers:

You chose a different formula to calculate the ETC and your result was "286.5". As you can clearly see, that value is not available in the 4 given answers. Therefore, this means that the formula you have chosen does not lead to a "correct" result - at least for this question.

So for the PMP Exam this means: If the formula you are using does not result in a number that is also available as one of the four answers, it means that you have selected the "wrong" formula. At least, it is "wrong" in the sense that it does not result in an available answer.

Does this last bit make sense?