Best Of 101Questions [4/21/12]

My five favorite listings on 101questions this week:

  • Soccer Ball Inflation, Nathan Kraft. My students are promiscuous with proportions, applying them to any situation where they have one known relationship and one unknown. That’s my fault. A proportions unit ought to feature unproportional relationships right alongside the proportional and in similar quantities. So here’s a good one from Nathan Kraft. If the small ball takes nine pumps to fill and it’s half the size of the large ball, the large ball will take 18 pumps. Right?
  • Swimming the River, Scott Farrar. Resultant vectors aren’t always easy to visualize, which makes this invaluable. If I used this in a class, I’d probably cut it halfway so students could calculate the girl’s odds of making it to the rock. Pairs well with Crosswind Landing.
  • Tuba Echo, Nathan Kraft. So you have a guy honking away on a tuba, facing a wall that honks back. Gold
  • Google Calc Error, Carl Malartre. For whatever reason these are pretty risky. Why is Carl at 80% with this while James McKee is stuck in Skipsville with Temperature Conversion?
  • Please take a seat, Gulliver, Statler Hilton. My question: “How tall is the person who would sit there? How much would she weigh?”

Plus my own listings:

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


  1. Mike Silvestri

    April 22, 2012 - 4:04 am -

    I’m loving these questions and the 101Questions site!
    These are fantastic Act 1 pics/videos, and the Act 2 information seems pretty easy to put together. Any advice on how to make an exciting Act 3 without a corresponding image? My students are working on area/volume now (grade 5) and I’d like to try the sod picture, for instance.

  2. Any plans to add the ability for people to contribute addendum videos/images/lesson plans/etc? For example, I just created a snapshot of the waveform of the tuba echo so I could figure out the time delay, and would love to be able to share that kind of thing easily.

  3. David,
    I’m trying to organize my videos on my wikispace ( and I would love that information ( I also took a snapshot of the parking lot with Google Earth and included the distance between myself and the building. (I love this problem. It’s such a cool way to talk about distance, rate, and time. Plus, I don’t really need the video. I can take my class outside and just do it, which is an even better way to grab their attention.)

    Thanks for the shout-outs. I think the soccer ball video is very similar to the gummy bear video. I tried the gummy bear problem with a student after school and we had a great discussion about using the heights of the gummy bears and the areas. It became very natural for the student to see that, in order to figure out how many gummy bears were in the super gummy bear, we would have to really find the volume of each. I didn’t have to explain anything to him…just had to ask the right questions at the right time. (We kind of got stuck since we didn’t know the depth of the gummy bear. Need more act 2 info.)

  4. I don’t seem able to add a question to the 101qs when you link directly to them… Is that intentional?

    The tuba video is great! I thought — How fast would he have to play Frere Jacques for it to sound like a canon? If he wants to slow it down, how far away can he stand and still hear the echo?

  5. @Mike, @David, at the moment, all we have are a bank of perplexing first acts. The second and third acts are where the work and the resolution of that work happens and they’re totally absent from at the moment. That won’t be the case forever.


    I don’t seem able to add a question to the 101qs when you link directly to them… Is that intentional?

    Yes. It’s only possible to add a question (or register a skip) from the homepage where the first acts are stripped of identifying information like the uploader’s identity and the uploader’s initial question. That’s designed to put all uploaders on equal footing and to capture a user’s response (either a question or skip) with as little bias as possible.