19 Apple Trees
Date: 06/29/2001 at 15:15:30 From: Johnson Truong Subject: Brain teaser I have a question that my teacher couldn't answer. We got the question at a math competition. You have 19 apple trees. How could you place them in 9 rows of 5? They gave us a clue: get outside of the box, starlight, starbright, first star you'll see tonight.
Date: 06/29/2001 at 15:49:26 From: Doctor Jaffee Subject: Re: Brain teaser Hi Johnson, I'll give you another hint. I was able to solve the problem by starting off with a six-pointed star (constructed with two equilateral triangles). See if you can work it from there and if you want to check your solution with me, write back. If you are having difficulties, let me know and show me what you have done so far, and I'll try to help you some more. Good luck. - Doctor Jaffee, The Math Forum http://mathforum.org/dr.math/
Date: 06/30/2001 at 17:47:11 From: Johnson Truong Subject: Brain teaser I tried that but I got only 7 rows.
Date: 07/01/2001 at 13:39:14 From: Doctor Jaffee Subject: Re: Brain teaser Hi Johnson, Your star should look something like this: A X / \ // \\ / \ F\---------------------------------/B \ // \ / \ / \\ // \ // \\// \ / /\ X // \\ // \ / \ / \\ // \\ E /--------\------------/------------ C \ // \ // \ / \ // \\ D Now connect A to D, then connect B to E, and finally C to F. If you drew everything correctly, those three segments should meet at a point in the center of the star. The 3 line segments you just drew plus the six sides of the star make 9 lines. There are 5 points of intersection on each line, and the total number of intersections is 19. For more, see the Math Forum's line puzzle at: http://mathforum.org/k12/k12puzzles/rosebush.puzzle3.html I hope this helps. Write back if any of my explanation requires clarification or if you have any other question - Doctor Jaffee, The Math Forum http://mathforum.org/dr.math/
Search the Dr. Math Library:
Ask Dr. MathTM
© 1994- The Math Forum at NCTM. All rights reserved.