I think Its a very good thing for you to do. Because for about three
month I ve been looking at this problem and thinking: "How
complicated it is..." Then I read what s on the board, and found out
that the example was WRONG. And solved it. I think no example would
be better than wrong example here...

Yeah, IMO this is wrong example. Maybe I don't get it, but...

"Let's choose 2 blanks with minimal numbers"
Does it mean "Let's choose 2 blanks with minimal length"??

Second line of the example:
Why is second blank sawed-off?? As I get it, chosen are blanks with lengths 2 and 3. Their lengths are therefore different and blank 3 should be sawed off (step 3 point 2). Oh, and I see that the length of sawed off piece is as long as other blank. But which one?? Longest, shortest?? Maybe picked up randomly ;]

Please reply.

I suggest to replace
"Let's choose 2 blanks with minimal numbers"
with
"Let's choose some 2 blanks"

Do you agree?