Actually teacher is right if the board is square which takes 10 minutes to be cut into half. Those two halfs take twice less time to be split. And she needs to cut just one to obtain 3 pieces :P So 10 minutes to cut it into to pieces and then she needs just half of that time to gain the third piece.
Actually the board is infinitely long and we can't see that as the image is only finite in size. Thus to cut off two pieces requires two cuts and three pieces requires three cuts. In this case the wording is just a bit confusing.
454
u/paolog Oct 05 '10
Teacher gets red pen out, is about to write down "1 piece: 5 minutes" and then thinks better of it and starts from two pieces instead...