Notes On Exercises

The information below is taken directly from Knuth, and gives contexts to the difficulty of problems found in his work:

Rating Interpretation:

00
An extremely easy exercise that can be answered immediately if the material of the text has been understood; such an exercise can almost always be worked "in your head."

10
A simple problem that makes you think over the material just read, but is by no means difficult.  You should be able to do this in one minute at most; pencil and paper may be useful in obtaining the solution.

20
An average problem that tests basic understanding of the text material, but you may need about fifteen or twenty minutes to answer it completely.

30
A problem of moderate difficulty and/or complexity; this one may involve more than two hours' work to solve satisfactorily, or even more if the TV is on.

40
Quite a difficult or lengthy problem that would be suitable for a term project in classroom situations.  A student should be able to solve the problem in a reasonable amount of time, but the solution is not trivial.

50
A research problem that has not yet been solved satisfactorily, as far as the author knew at the tie of writing, although many people have tried.  If you have found an answer to such a problem, you ought to write it up for publication; furthermore, the author of this book would appreciate hearing about the solution as soon as possible (provided that it is correct). 

>      Recommended
M     Mathematically oriented
HM  Requiring "higher math" 

Note: It is unlikely that the problems on this blog will go into the 50's.