I was never a big fan of these types of problems on standardized tests when I was younger but the more you analyze the problems, the better your reasonable skills should eventually become.
Take this problem for example this image below. Can you determine which one is the odd one out?
The answer is after the fold.
The trick into solving this might be figuring out which one is the least special.
If your first guess was going to be the second one because it is the one without a frame, that would be the one reason it is not the odd one one out.
Fair enough but it could be very common for you to say that the green square sticks out as being different but that is its reason for being special — it is the only non-red item in the set.
After that you might say, the third one which is the only circle in the set of 5 images. That again would be the only reason to differentiate it from the rest.
The last incorrect answer would then be the small red square at the end. It is the only one that is not the same size as the four that went before it.
So by process of elimination, it must be therefore be the first one. The answer is not which one is special but rather it is the one that is the least special one selected as the odd one out.
Go ponder on that for a while.
Source: Tanya Khovanova’s Math Blog