• Pizza Doubler. The initial problem gives specific dimensions, but the momentum of the problem should be towards a general argument.
• Coin Carpet. If you’re going to carpet your floors with any kind of US bill, obviously one-dollar bills get you the same area for the lowest price. But what about coins? If I had a classroom, this problem would run all year. I’d put a bounty on the best coin from around the world. (Something like the slope challenge.) “You found some saucer-sized coin from some obscure island with very favorable exchange rates? Pin the picture to the wall, kid. Nice work.”
• Leaky Faucet. I needed this one for PD purposes. As an exercise in rates goes, it’s fairly generic, though I wouldn’t have guessed anywhere close to the answer.
• Fry’s Bank. Timon Piccini posted this video to 101qs.com and I wanted to build a sequel around it.

Featured Comment

My students were amazed by the Fry’s Bank problem. My favorite part was when a student left out a zero and accidentally calculated the balance after 100 years. \$8 after 100 years, but 4 billion dollars after 1,000 years. I had to try it on a different calculator to make sure that his calculator wasn’t broken.

I'm Dan and this is my blog. I'm a former high school math teacher and current head of teaching at Desmos. More here.

1. #### Randy

May 2, 2012 - 6:31 pm -

Well with respect to the Fry’s Bank question… He ought to be glad he doesn’t have his money in my bank. At 0.01% interest after 1000 years he would have a whopping \$1.03. Even my credit union account at the grand rate of 0.4% for the money market account would land him a nice sum of only \$50.37. Oh bring me back the good ol’ days when banks were required by law to have 5.25% Well maybe I don’t want the good ol’ days back, but I wouldn’t mind a nice solid interest rate right now.

2. #### Bob Lochel

May 3, 2012 - 3:52 am -

I love the Fry’s Bank Account video. Just shared it with my Algebra I teachers, who are currently working through exponential growth models.

The “beep” reminds me of Jimmy Kimmel’s “this week in Unnecessary Censorship”. My bank just started doing colonic scans…..surprisingly refreshing…..

3. #### Jenn Blalock

May 5, 2012 - 11:32 am -

This sets up a perfect sector area question:

Major League Eating http://www.ifoce.com/records.php is the undisputed authority on competitive eating worldwide. All official eating contests are sanctioned by MLE and MLE maintains all official eating records. Following are recent records:

24″ Pizza
7 1/2 Extra Large Bacci Pizza Slices
15 Minutes/ July 9, 2005
Richard LeFevre

16″ Pizza
47 Slices Big Apple Pizza/Battle at the Big Apple World Pizza Eating Championship
10 Minutes/November 8, 2008
Patrick Bertoletti

(Further information Patrick Bertoletti is 2nd ranked competitive eating behind Joey Chestnut – Nathan’s Hot Dog Eating Champion; Joey Chestnut ate 45 slices in the 16″ competition)

4. #### Dan Henrikson

May 5, 2012 - 1:08 pm -

My students were admazed by the Fry’s Bank problem. My favorite part was when a student left out a zero and accidentally calculated the balance after 100 years. \$8 after 100 years, but 4 billion dollars after 1,000 years. I had to try it on a different calculator to make sure that his calculator wasn’t broken.

5. #### Michael Serra

May 8, 2012 - 4:23 pm -

Dan, I loved the simplicity of the pizza coupon activity. I think the idea of using coupons, or having kids come up with clever coupons is ripe for further exploration.
Thanks. I’ve always loved pizza problems in class and this will add a new dimension.

6. #### Nathan Kraft

October 7, 2012 - 5:11 pm -

I’m really digging up some old 3-acts now.
I just worked out Fry’s Bank Account using Microsoft Excel and noticed something odd.
At first I ran the numbers and got the same answer as the act 3 video. But I noticed that the money was not rounding off to the nearest cent every year. Wouldn’t banks do that? So I changed my formula to round it ever year and got a different answer (4.2 billion instead of 4.3). Which one is right?
I’m going to get to the bottom of this…at least before I do it in class.