3×3

by Nuno Rocha, 6 mins, Portugal, 2010
A night watchman and a janitor meet unexpectedly on a basketball court.

Bay Area International Children’s Film Festival

1621: A New Look at Thanksgiving

by Catherine O’Neill Grace

Four Fours

Beremiz shows how to make each of the numbers from zero to ten by combining exactly four 4s.

The Man Who Counted by Malba Tahan: Ch.7: Going to Market

Brazil 4 maths – The Definitive Four Fours Answer Key

Four fours is a mathematical puzzle. The goal of four fours is to find the simplest mathematical expression for every whole number from 0 to some maximum, using only common mathematical symbols and the digit four (no other digit is allowed).

Buying Turkeys

A man bought a number of turkeys at a cost of $60.00, and after reserving fifteen of the birds he sold the remainder for $54.00, thus gaining 10¢ a head by these.
How many turkeys did he buy?

536 Puzzles and Curious Problems by Henry Ernest Dudeney

Shopping Spree

Timothy spent all his money in five stores.
In each store, he spent $1 more than half of what he had when he came in.
How much did Timothy have when he entered the first store?

100 Numerical Games by Pierre Berloquin

10 Bags of Coins

Ten bags are full of coins. All the coins look the same, but those in one of the bags weight 1 gram less than those in the other nine bags. You have a scale like the one shown in the picture, but are permitted to make only one weighing. Any number of bags will fit on either side of the scales.

How do you find out which bag contains the lighter coins?

It’s the Friday Puzzle!
Ten Bags of Gold
Weighty Problems

12 Coins

You have 12 identical-looking coins, one of which is counterfeit.
The counterfeit coin is either heavier or lighter than the remaining 11.
Can you find the counterfeit coin with only three weighings?

Cut the Knot: The Oddball Problem, Weighing 12 coins…
Solution for the “12 Coins” Problem
Weighty Problems

The Nine Coins Puzzle

Suppose you have nine identical coins that all look alike. You also know that all coins are identical in weight except for one, which is lighter than the others, the counterfeit. The difference is only perceptible by using a special balance, but only the coins themselves can be weighed, and it can only be used twice in total.

Can you find the counterfeit coin with only two weighings?

 
 

Balance puzzle
Weighing 9 Balls

The 9 min Pasta Timer Puzzle

It’s the Friday Puzzle!

Today I have to make dinner and have to boil some pasta for exactly 9 minutes. However, I only have two hourglasses. One of them measures 7 minutes and the other measures 4 minutes.
Can I use the hourglasses to time exactly 9 minutes?

Seven Socks

There are 7 red socks and 7 white socks in a drawer. If you must reach in the drawer blindfolded, what is the least number of socks you must pull out of the drawer so that you get either two reds or two whites?

Fractals, Googols, and Other Mathematical Tales by Theoni Pappas
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