Boris A. Kordemsky: 8 puzzles worth knowing

8 puzzles from Boris A. Kordemsky, each explained in a minute and credited to the original work. Free on Savvy.

Every sister has as many brothers as sisters; every brother has double that in sisters
In one family, each daughter has exactly as many brothers as she has sisters, and each son has exactly twice as many sisters as he has brothers. How many sons and daughters are in …
— Boris Kordemsky, The Moscow Puzzles: 359 Mathematical Recreations
A clockmaker's apprentice fitted two identical hands — and broke every reading
An apprentice repairing a clock accidentally fits two hands of identical length and appearance, so there's no way to tell which is the hour hand and which is the minute hand just b…
— Boris A. Kordemsky, The Moscow Puzzles: 359 Mathematical Recreations
The Diesel Ship and the Seaplane
A diesel ship sets out on a long voyage. When it's 180 miles from shore, a seaplane — flying exactly ten times as fast as the ship travels — is sent out from shore to deliver the m…
— Boris Kordemsky, The Moscow Puzzles: 359 Mathematical Recreations
Kordemsky's five apples in a basket
Five apples sit in a basket. Can you divide them among five girls so that each girl receives an apple of her own - and yet one apple is still left behind in the basket?
— Boris A. Kordemsky, The Moscow Puzzles: 359 Mathematical Recreations
A clock takes 30 seconds to strike six — how long to strike twelve?
A wall clock strikes six o'clock, and you time it: exactly 30 seconds pass between the first stroke and the last. At the same steady pace, how many seconds will the same clock take…
— Boris Kordemsky, The Moscow Puzzles
Which way did the bicycle go?
A bicycle rides across a patch of wet sand, leaving two overlapping tire tracks — one from the front wheel, one from the rear. The two curves cross each other several times, and ne…
— Boris A. Kordemsky, The Moscow Puzzles
Kordemsky's Two Passing Freight Trains
Two freight trains, each a sixth of a mile long, travel toward each other at 60 mph apiece. From the instant their locomotives draw level to the instant their cabooses do, how many…
— Boris A. Kordemsky, The Moscow Puzzles: 359 Mathematical Recreations
Ten Chairs, Four Walls, an Equal Number on Each
A rectangular dance hall has four walls. Place exactly ten chairs along them so that every one of the four walls has the same number of chairs standing against it. No cutting chair…
— Boris A. Kordemsky, The Moscow Puzzles: 359 Mathematical Recreations

Boris A. Kordemsky: 8 puzzles worth knowing

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