April 2020 April 2020 | Page 6


Two trains, 200 km apart, are moving toward each other at the speed of 50 km/hour each. A fly takes off from one train flying straight toward the other at the speed of 75 km/hour. Having reached the other train, the fly bounces off it and flies back to the first train. The fly repeats the trip until the trains collide and the bug is squashed. What distance has the fly traveled until its death? There is a complicated and an easy way to calculate this cool math puzzle. Think outside the box. Good luck!

This is one of the most famous logic problems which can be solved by using classic logic operations. You may have heard a few variations of this puzzle before (e.g,. 2 doors - 1 to heaven and 1 to hell) but still, it's one of the best brain teasers.

There are a few types of logic questions:

1. Direct question: "Hello there beauty, what would your sister say, if I asked her where this road leads?" The answer is always negated.

2. Tricky question: "Excuse me lady, does a truth telling person stand on the road to the village?" The answer will be YES, if I am asking a truth teller who is standing at the road to village, or if I am asking a liar standing again on the same road. So I can go that way. A similar deduction can be made for negative answer.

3. Complicated question: "Hey you, what would you say, if I asked you ...?" A truth teller is clear, but a liar should lie. However, she is forced by the question to lie two times and thus speak the truth.


Kevin Garvey, PE, Wright-Pierce

Aaron Wolfson-Slepian, EIT, JSN Associates, LLC

Max Fischer son of Joel Fischer, PE

Cranium Challenge

March Solution

Please send you answers to

Thomas Selling via e-mail: [email protected]

Correct responses will be recognized in the future issues of the New Hampshire Civil Engineer.

April Challenge