Enigma: Imaginary journeys

时间:2019-03-01 06:15:03166网络整理admin

By KEITH AUSTIN THIS map of Imaginaria shows the four junctions, A, B, C and D, and the six roads, AB, AC, AD, BC, BD and CD. The two roads that are dotted have flower verges and the other four roads have grass verges. I am now imagining that I am standing at the midpooint of one of the roads and facing in one of the two directions the road goes. You are now to give me the instructions for a journey; you give me three words in order and each word is left or right. I follow your instructions in turn at the three junctions I come to on my imaginary journey. When I have followed your last instruction I stop half way along the road I am on and tell you whether I have a flower verge or a grass verge. I then imagine myself back at my original starting position, you give me another journey and I repeat the exercise. We continue in this way until you can deduce what my starting point is and which direction I face. For example, if I imagine I am on AC, facing C, and you say left-right- right then I will go onto CB, BD and stop on DC. So I will tell you I have a grass verge. What is the minimum number of journeys I must allow you to give me in order that you can be certain of finding my starting point and direction? A £10 book token will be awarded to the sender of the first correct answer opened on Thursday 17 November. The Editor’s decision is final. Please send entries to Enigma 793, New Scientist, King’s Reach Tower, Stamford Street, London SE99 0BB. The winner of Enigma 788 was Peter Vogel of EPSE, the Netherlands. Answer to Enigma 788 Count and count (a), (b), (c), (d) and (e), that is,