I use S2000Magician’s excellent “dollar beta” and "dollar duration method for adjusting beta and duration (see here:
Anyway, in the 2012 AM exam, this would have given an answer inconsistent with CFAI’s answer, as they do the two step method (adjusting the value of the portfolio, then the beta of the portfolio), round each, and then add. Whereas S2000Magician’s method (more correctly) rounds at the end. In this example, you get an answer different by 1 contract.
Do I need to worry about this? You can even see in the guideline answer that CFAI have kind of screwed up because they’re acknowledging that you have to add together the amount of contracts you have to buy for each step, and if you use their unrounded numbers, you get the same answer that I got. It’s just if you round and then add, you get 1 contract fewer.