Diminishing Returns From Studying And Purchasing Speakers

Personally, studying for me is practically non-existent.  In those rare cases where something is forgotten, I typically skim through all of my notes and find the one thing that I'm forgetting, along with anything I happen to skim through.  In my case of studying, a graph would look similar to an upside down check mark, where for the first 30 seconds of skimming through notes are increasingly productive, up until the point where I find the specific information I'm looking for.  From that point forwards, my curve, which wouldn't end up being much of a curve, would shoot down until the point where I am no longer looking at my notes.  For this very impractical example, at the VERY beginning, studying is extremely effective, up until I find what I need, then if not immediately, the knowledge gained from the studying falls, as if from a high cliff.  This proves (somewhat) the Law of Diminishing Returns true.

Another (better) example where the Law of Diminishing Returns holds true would be dB level from additional speakers.  Buying the first speaker would set your starting decibels at 80 dB, for the purpose of this example.  Buying a second speaker would double the perceived volume, which would result in the +10 dB bringing up the total volume to 90 dB.  Buying a third speaker wouldn't double the perceived volume, but a fourth speaker would.  The third speaker would result in a +6.66 dB increase, and the fourth a +3.33 dB increase, bringing the total to 100 dB.  Any additional speakers after that wouldn't be worth the money for such a small increase of dB level.  If you were to continue purchasing speakers, the money would just be wasted, and the returns would decrease because the money spent isn't worth the dB increase (if any at all) anymore.  Whenever the costs (speaker cost) outweigh the benefits (dB increase), then you know it is time to stop purchasing that item (speakers).