This is a wonderful website offering a long list of interesting and challenging math and computer science problems.
There are many different kinds of problems to solve: some are purely mathematical in nature, and some would be considered more like pure computer science.
Some are easy (“What is the 1001st prime number?“), some seem moderately challenging (“What is the sum of the digits of 
The problems are freely available, but it looks like you have to register to submit answers.
Through Math for America, I am part of an on-going collaboration with the New York Times Learning Network. My latest contribution, a Test Yourself quiz-question, can be found here:
https://learning.blogs.nytimes.com/2012/02/27/test-yourself-math-feb-27-2012/
This problem is based on the unlikely emergence of basketball star Jeremy Lin. How unlikely was his inaugural 7-game winning streak?
Inspired by a recent foray into Piggy Bank Estimations, I started thinking about the following question: how are coins distributed? That is, what percentage of coins in a collection of random change are pennies? Nickels? Dimes? Quarters?
I began with two assumptions. They are debatable, like most assumptions are, but they seem like a good place to start an investigation:
1) Every amount of change is equally likely to be received.
2) Every amount of change is provided using the minimum number of coins.
What (1) means is that you are just as likely to get 13 cents back in change as you are to get 91 cents when you purchase something. And (2) means that, when you get that 91 cents back, you’ll get it as 3 quarters, 1 dime, 1 nickel, and 1 penny; not 4 dimes, 9 nickels, and 6 pennies.
I made a chart in Excel of all the possible change amounts from 1 to 99. I then figured out how many of each coin would be used to provide that amount of change, assuming that change was given efficiently.
Now, assuming each change amount is equally likely, we can simply count the total number of coins and then figure out each percentage as a share of that total. The total number of coins in the list is 466. The number of each coin, and it’s approximate percentage, is given below.
By this analysis, a large, random collection of coins should be roughly 42.5% pennies, 8.5% nickels, 17% dimes, and 32% quarters. Do me a favor: the next time you find yourself sitting on a big pile of change, see how it stacks up against these numbers and let me know.
And if you like, you can check this theoretical ratios against the actual numbers in my Piggy Bank.
Here’s a nice little quiz on plotting points in the Cartesian plane:
http://www.thatquiz.org/tq/practice.html?idpoints-j8-l5-m2kc0-na-p0
After you’ve warmed up, be sure to try plotting complex numbers, or test your knowledge of the Polar plane (in both degrees and radians).
There are a number of simple little quizzes to enjoy at thatquiz.org; just be careful not to let the day slip away!
Today we celebrate our second Permutation Day of the year! I call days like today permutation days because the digits of the day and month can be rearranged to form the year.
We enjoyed our first permutation day of 2012 just 21 days ago. Exactly three weeks apart! That seems unusual. I also wonder “How close could two permutation days be?”
Celebrate Permutation Day by mixing things up! Try doing things in a different order today. Just remember, for some operations, order definitely matters!