The Logical Puzzle - 29 Apr 2008

Solution to April’s Puzzle: Suicidal Mosquito

Two trains drive toward each other on the same rail. Both trains drive at a speed of 100MPH. When the trains are 100 miles apart, a mosquito starts flying back and forth from the front of one train to the other at a speed of 200MPH. What total distance will the mosquito cover before the two trains crash?

For some people the puzzle might seem to require infinity calculations. Although solving the puzzle this way is possible, such a solution is unnecessarily complicated. The simplest way to think about the puzzle is to consider only duration and speed. The time it takes until the trains crash is half an hour, and the speed of the mosquito is 200MPH. With such speed and duration, the mosquito would cover 100 miles.

May’s Puzzle: A Cat, a String, and the Earth

This month’s puzzle is quite simple, but I like it because it’s so counter intuitive. Suppose you lay a string on the ground all around the earth right over the equator. The length of the string would be equal to the earth’s equatorial circumference—40,075.02 kilometers. Then, suppose you add 1 meter to the string, and suspend the string directly above the equator, with an even distance from the ground all the way around. Would a cat be able to pass from one hemisphere to another below the string?

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