I wanted to add some memory to my 2011 Macbook Pro 15", so I bought a 8GB piece. Can I add the 8GB to 1 slot and have a 4GB or 2GB stick in the other slot? On the Apple site it says keep them equal and 8GB max, so I want to check here because many people are reporting using 16GB. I only bought 1 8GB piece so I'd like to use it without having to buy another, and I assume my laptop currently has 2 2GB pieces, 2GB in each slot. Thanks.