Hi Julia,
this is one of those never ending debates in sudoku circles. There are some puzzles that require some detailed logical steps to crack them and some people suggest you may as well guess. Also the way some of these logical arguments are presented suggests that a guess was made to arrive at the solution (whenever an argument is presented like this I'm convinced there is another 'pattern based' argument that doesn't involve guessing).
To get a more detailed solution for a particular puzzle you're stuck on post the puzzle in the 'help with particular puzzles' section and someone will post what techniques you need to crack the puzzle. Alternatively download some solver software and put the puzzle in that.
I doubt the brain age puzzles require very difficult techniques. Sometimes you miss the obvious