You have fifty quarters on the table in front of you. You are blindfolded and cannot discern whether a coin is heads up or tails up by feeling it. You are told that x coins are heads up, where 0 < x < 50. You are asked to separate the coins into two piles in such a way that the number of heads up coins in both piles is the same at the end. You may flip any coin over as many times as you want.
You have 12 black socks and 12 white socks mixed up in a drawer. You’re up very early and it’s too dark to tell them apart. What’s the smallest number of socks you need to take out (blindly) to be sure of having a matching pair?
Three socks. If the first sock is black, the second one could be black, in which case you have a matching pair. If the second sock is white, the third sock will be either black and match the first sock, or white and match the second sock.
A man hiked through the woods with his dog and saw three coyotes, six wolf cubs, seven bunnies, nine squirrels and thirteen chipmunks. How many total feet were there?
Early one morning Hal, the owner of a hardware store, sells a mailbox for $25 to Courtney that cost him $20 wholesale. Courtney pays with a $100 bill and Hal discovers he doesn’t have enough change. He runs to the jewelry shop next door, where Jack, the owner, gives him change in exchange for the $100. Later that afternoon, Jack discovers the $100 bill is a counterfeit and Hal pays him $100 to make it right.
The total loss was $95.
-$20 = The wholesale cost of the mailbox
$100 = The money from Jack
-$75 = The change paid to Courtney
-$100 = To pay Jack back
-$20 + $100 – $75 – $100 = -$95
It’s easy to think Hal lost $195 but that fails to account for the $100 used to make the change, which came from Jack, not Hal. Jack paid $100 in exchange for a worthless piece of paper, so the $100 was initially Jack’s loss. Hal had made a $5 profit until Jack’s discovery. If you guessed $100, that’s arguably correct, but not making $5 in profit isn’t a loss in the strictest sense of the word.
A similar problem can be found in L.A. Graham’s Ingenious Mathematical Problems and Methods with a range of 1 to 9, but the principle remains the same – the numbers with the smallest difference produce the largest product. You start out with the highest two digits, 7 and 6, then attach 5 and 4, putting the smaller of the two digits with the larger number, giving you 74 and 65. The next two highest digits are 3 and 2, giving you 742 and 653. Finally, you add the 1 to the lower number. Page 80 has the details of that solution.
Mario, from Super Mario Brothers video game by Nintendo. He roams the land searching for the princess and his primary method of getting rid of folks is to stomp on them.
