## Kaprekar’s constant

A student talked about Kaprekar’s constant (6174) during their my favorite presentation. Really cool. Steps (from wikipedia): Take any four-digit number, using at least two different digits. (Leading zeros are allowed.) Arrange the digits in descending and then in ascending order to get two four-digit numbers, adding leading zeros if necessary. Subtract the smaller number […]

## Lizard Grow

My son was given this lizard as a big brother gift (can’t find online link to product, but here’s a similar toy). Thoughts? Original Size Size After 2 Day Soak Before Measurements Left image Length: 905 pixels Width (between front feet): 275 pixels 1 inch: 90 pixels Right image Height: 150 pixels 1 inch: 115 […]

## World’s Greatest Drag Race 3!

See also: World’s Greatest Drag Race 1 (with lesson) World’s Greatest Drag Race 2 Classroom action from my 180 photos blog Drag race page on 101qs.com

## Final Oreo Post

Part 1 and Part 2. There have been a couple of questions regarding the validity of my measuring process. The one that irked me the most was the fact that I had never measured the weight of the wafers of the Double Stuf. Was it possible that the wafers for the Oreo and Double Stuf […]

## Oreo Verification

So things have gone a bit crazy lately. While on summer vacation, this happened: All for a blog post that I wrote in February. (My previous high for views in one day was 299.) In the original post where my class suggests that the Double Stuf Oreo is only 1.86x stuffed, the data set is […]

## Powers of 2 without a Zero

2^86 is largest known pwr of 2 that does not contain 0.What about other digits?Does each non-zero digit occur inf often among the pwrs of 2? — James Tanton (@jamestanton) March 6, 2013 Interesting. The Intro to Programming Students gave a crack at this one; and after 30 minutes all were close and half had […]

## Reducing Prime

Number theory nugget: 357686312646216567629137 is a prime number which remains prime after removing any number of digits from the left side! — Maths World UK (@MathsWorldUK) March 4, 2013 Otherwise known as left-truncating primes with every suffix prime and no digit are zero. Here is the whole sequence. It was proven that 357686312646216567629137 is the last […]

## Oreo: Original vs. Double vs. Mega

[edit 8/20/13: New post with more data on the weights of Oreos and Double Stuf Oreos.] [edit 8/21/13: And Part 3.] Are Double Stuf Oreos really double stuffed? Some disagreement here: Chris Danielson in part 1 2 and 3 versus Chris Lusto in part 1 and 2. Enter in the Mega Stuf Oreo. Is the Mega Stuf double stuffed, triple stuffed, more???? […]

## Meteor Go Boom

How far away is the meteor from this security camera when it explodes?