[Pseudocontext Saturday] Blimp

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Team Commenters: 0

Come on, team. This is your week.

This Week’s Installment



What mathematical skill is the textbook trying to teach with this image?

[poll id=”4″]

(If you’re reading via email or RSS, you’ll need to click through to vote.)


Every Saturday, I post an image from a math textbook. It’s an image that implicitly or explicitly claims that “this is how we use math in the world!”

I post the image without its mathematical connection and offer four possibilities for that connection. One of them is the textbook’s. Three of them are decoys. You guess which connection is real.

After 24 hours, I update the post with the answer. If a plurality of the commenters picks the textbook’s connection, one point goes to Team Commenters. If a plurality picks one of my decoys, one point goes to Team Me. If you submit a mathematical question in the comments about the image that isn’t pseudocontext, collect a personal point.

(See the rationale for this exercise.)

Pseudocontext Submissions

Cathy Yenca


David Petro




The judges rule that this problem satisfies the first indicator of pseudocontext:

Given a context, the assigned question isn’t a question most human beings would ask about it.

The judges wager that if you lined up 100 arbitrary human-types and asked them the first question they wonder about this context, no more than two of them would ask about how long the ping pong ball is in air.

The judges get the sense that the author of the problem just needed some projectile — any projectile — for the task of calculating total time in air. The tennis ping pong ball [Thanks, Paul Hartzer. -dm], the number drawn on the ping pong ball, and the prize you win for catching the ping pong ball — those are all unrelated to the mathematical work. That’s pseudocontext.

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. “If the flying Karamazov brothers hang out to watch the game, how many of them need to stand on the kid in yellow’s shoulders to reach the blimp.”

    I’m sure that’s it.

  2. The most obvious ones to me are subtracting integers and calculating parabolic motion. But “subtracting integers” seems like too easy a process for this image, so I’m going with “parabolic motion”. In my experience, the parabolic story problems often involve someone standing on a cliff and throwing something into the air. How long until it reaches the ground?

    But I was wrong last week. :D

  3. Only came to warn about this: the previous Pseudocontext Saturday post is under “uncategorized”. Oh, and I guess we can’t measure Becky because she’s happily impaled in a right triangle

  4. Each row of seats is 75 cm higher than the previous. How high is the ballon from the fan holding the string? Or maybe it’s dropping something? How long does the boy have till the bobblehead reaches him? [This dropping seems likely. Wish I had chosen parabolic motion.]

  5. What is the likelihood that little Johnny is about to catch a Wildcats t-shirt, only to be disappointed that it’s a size XXL?

  6. Maybe Jimmy is hoping some fine math student will write a linear equation describing the motion of his mini blimp which rose to a height of 45 feet at a constant rate for some amount of seconds? Note 1, mini blimps, like drones, are not permitted in stadiums. Note 2, Cubs tickets and the stubhub shutdown controversy would make a cool fall stadium problem…”Descibe the rate of change in World Series tickets sold online between the end of game 2 and the first pitch of game 3.”

    • Isn’t this pseudocontext as well? I admit I don’t know anything about the stubhub shutdown, but I can’t imagine why anyone would calculate this rate of change unless it’s explaining why the website got shut down. Can you clue me in?

  7. I don’t know the relevant numbers, but a problem I would legit be wondering in this situation is, how many people can read the writing on the blimp? (relevant facts: visual field arc-length of minimum letters a person can read; size/shape of the stadium)

  8. Michael Paul Goldenberg

    October 30, 2016 - 5:17 am -

    How long before the fans who are about to be lifted to heaven by The Rapture are at the same height as the blimp?

  9. Pseudocontext is not the right word for the Sydney question. More “awkward conversation between 2 people where one desperately wants to connect everything that is discussed to mathematics.”

  10. Another comment before Dan updates…

    I’m still having trouble deciding whether that white line is meant to be a string or just an invisible height line. If it’s a string, then most obvious question would be “how long is the string?” but that would be the easiest of the three measurements to take. That could be the pseudocontext here.

    Your fans await, Dan… ;)

  11. A much more interesting exploration of the Sydney Harbor Bridge would be to take a picture, put it in Desmos and approximate a quadratic equation to fit the arc. Use the roadway to be the x axis and find out the altitude to the top of the arc and maybe even how far those tiny tiny people have to walk when they climb it from one end to the other. Then, most importantly, figure out why people “Down Under” drive on the left side of the road and not the right.

  12. At least the Sydney Harbour Bridge problem makes it more difficult to Just Google It, since the question asks about the length of the bridge, but the answer (503 m) is actually the span length. The full bridge length is more than twice that length. ;)

  13. Now that the answer has been posted, I’ll casually note that the ping pong call is such a McGuffin that the judges didn’t even correctly describe it. ;)