Last minute coupons: 5 websites to check before buying anything
I'm shocked at how many people pay full price. There are tons of free coupons you can find online, meaning savings are just a click and a promo code away. I now make it a point to diligently check coupon sites before I buy anything online. Below are 5 of the big sites ...

A fun number elimination game: who will win?
Bored at the airport, Alice and Bob decide to play the following mathematical game. Alice writes the numbers 1, 2, . . . , N on a piece of paper. Bob goes first, and he picks two numbers x and y from the list. Bob crosses out these numbers from the ...

Geometry puzzle: string cutting game
This is a great problem I came across, and I'd love to see it used as a consulting or technical interview question. Here is the setup. An interviewer gives you a string that measures 4 meters in length. The string is to be cut into two pieces. One piece is made into ...

I know how much money you are carrying – why the math trick works
I don't usually like generic email forwards, but I make an exception for ones that involve math tricks. A couple years ago I got an email about how a waiter could calculate your age using "restaurant math." It was an interesting trick and I posted about how the it worked: see ...

How to enter a rebate when tracking expenses
Occasionally, I will get office supplies or food items with significant mail-in rebate discounts. What's the proper way to input the savings when you are tracking expenses? I will share my tactic below. (On a related note: I should mention I have never once had a rebate declined, in contrast to the horror ...

3 ways sleeping can help you get rich and save money
[Editorial note: I have posted the solution to the Monday puzzle in my comment here] At Stanford and in my office job, most people viewed sleep as wasted time. They would have preferred the time to be spent studying, exercising, or simply doing anything else. In fact, some people did just ...

Motivating a gym class using game theory
One of my favorite parts about writing this blog is hearing stories of how people have used game theory in real life. The other day I got an email from Jimmy who noticed game theory in action while at a group exercise class. Here is his story: Hey Presh, Thanks for taking the ...

Puzzle: optimal guessing in a card game
You and a friend play a guessing game with cards. The deck consists of four black cards and four red cards. The game is played as followed. You announce a guess of a card, and then your friend flips over the card on the table to see if you are correct. The ...

8 interesting tip jars
When I go out to the bars, I happily to shell out a dollar or two per drink for tip. But I do appreciate when a place puts some effort into making its tip jar distinctive either by making me chuckle or having a good style. Here are pictures of 8 different ...

5 ways Bing can help you save money
Until about two months ago, I exclusively used Google as my search engine. But I was curious about Bing because I heard it offered rewards for trying it out, and I'm a sucker for free money. I have to say I'm glad that I gave Bing a try. While Bing was ...

Stop fooling yourself: a better blind taste test that can help you save money
image by tiarescott Do you have strong preferences for food and drink? One of my friends insists on drinking high end vodka. Another prefers the taste of brand name cereal. And someone else drinks organic milk primarily for its taste rather than for health reasons. These specialty products can run up to ...

Coin flipping game: how to make a fair toss from an unfair coin
Alice and Bob play a game as follows. Alice spins a coin on a table and waits for it to land on one side. If the result is heads, Alice wins $1 from Bob; if tails, Alice pays $1 to Bob. While the game sounds fair, Bob suspects the coin may be biased ...

Probability puzzle: what are the odds of a bad password?
The other day I got an email about an interesting probability problem: Hi Presh - I'm a regular reader of your site and I came across a question which has bugged me the last couple of days. The problem is as follows: A system has 100 accounts, two of which have bad ...

7 travel essentials for the bald man
I first shaved my head about four years ago, and I've been enjoying the sleek and clean look. The style is full of practical advantages. A few that come to mind are: I never have to pay for haircuts, I can take extremely quick showers, and I no longer rely on ...

An easy birthday puzzle
image by y2bk Have you ever celebrated your birthday in another time zone? There's some novelty to it, as you can celebrate both during local time and your "home" time as you please. This sort of unusual time accounting can translate into a few extra hours of celebration. My friend loves doing this, ...