There are about 10 times more questions in the JAA question banks compared to the FAA. I wonīt say that it is impossible to memorize the questions, but you will have to study some material. Besides, many authorities change the questions a little bit, or they change a word here or there so the answer changes completely, so in some subjects you really need to learn the material.
I did my best to learn the material, and I didnīt even have to study for certain subjects such as GNAV, Radio Nav, Flight Planning, Mass and Balance, Instruments, and Aircraft General Knowledge. Your mileage may vary.