***you aren't learning much about plc's.***
Beg to differ, but skipping the basics is not in the interest of aspiring programmers... One might learn enough to troubleshoot the odd PLC program, but he/she won't gain an intimate knowledge of Boolean operations if they don't, or can't work through little challenges such as this... This material is at the heart of all programming languages, and whether you apply it using assembly language instructions, VB logical instructions, or ladder logic instructions, etc.,,, the task is the same, and learning how to solve such puzzles is key to becoming a good programmer... Anyone can use a TON timer, or a Do-Every-Thing instruction, but can you make 3 lights flash in sequence in response to a switch closure using assembly language... If you take up the challenge that this instructor has set out for the students, you just might learn enough to tackle such a problem in any language, on any computer.... Remenber that the WhizBangDoEverthing instruction is only available on Acme PLCs and it's not truly an instruction but rather a built in routine...kinda like the "Move to Perch" instruction in GMF/Karel... Of course you could write your own if you knew the basics...
The most difficult programming instructions to learn are the basic ones, and most people simply skip over the basics if given a chance... Obviously our guest has an instructor who isn't about to allow that, and the challenge is clear...
Picture yourself connected to a PLC2 family processor which lacks an OSR instruction..
Limit yourself to the basic relay instructions (XIO, XIC,OTE,OTL,OTU), and now you will have to think!!!
Of course that may be just what the instructor had in mind...
BTW... telling the student to do a search for a solution that he/she can simply copy has it's flaws also....
PS: I'm not the instructor..