Posts filed under ‘123’
by Nuno Rocha, 6 mins, Portugal, 2010
A night watchman and a janitor meet unexpectedly on a basketball court.
Beremiz shows how to make each of the numbers from zero to ten by combining exactly four 4s.
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).
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?
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?
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?
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?
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?
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?