Entries Categorized as 'Mathematics'
October 31, 2016
Gaga ball pit under construction.
A couple middleschoolers decided to build a gaga ball pit for their interim project. Since they’d already had their plan improved and I’d picked up the wood over the weekend, they figured they could get it done in a day or two and then move on to other things for the rest of the week. However, it turned out to be a bit more involved.
They spent most of their first day–they just had afternoons to work on this project–figuring out where to build the thing. It’s pretty large, and our headofschool was in meetings all afternoon, so there was a lot of running back and forth.
The second day involved some math. Figuring out where to put the posts required a little geometry to determine the internal angles of an octagon, and some algebra (including Pythagoras’ Theorem) to calculate the distance across the pit. The sum a^{2} + a^{2} proved to be a problem, but now that they’ve had to do it in practice they won’t easily forget that it’s not a^{4}.
Mounting the rails on the posts turned out the be the main challenge on day three. They initially opted for trying to drill the rails in at an angle, but found out pretty quickly that that was going to be extremely difficult. Eventually, they decided to rip the posts at a 45 degree angle to get the 135 degree outer angle they needed. We ran out of battery power for the saw and our lag screws were too long for the new design, so assembly would have to wait another day.
Finally, on day four they put the pit together. It only took about an hour–they’d had the great idea on day three to put screws into the posts at the right height, so that they could rest the rails on the screws to hold them into place temporarily as they mounted the rails. By the time they added the final side the octagon was only off by a few, easily adjusted centimeters.
They did an excellent job and noted, in our debrief, just how important the planning was, even though it was their least favorite part of the project. I’d call it a successful project.
Citing this post: Urbano, L., 2016. Gaga Ball Pit, Retrieved February 26th, 2018, from Montessori Muddle: http://MontessoriMuddle.org/ .
Attribution (Curator's Code ): Via: ᔥ Montessori Muddle; Hat tip: ↬ Montessori Muddle.
Posted in Experiential, MathematicsNo Comments »  Tags: algebra, geometrys, interim project, makerspace
August 29, 2016
Our PE teacher just started up an archery program at school (first classes today actually), and she shared this video with me that seems like it might be useful in geometry class. Specifically, it uses circle packing to estimate the relative difficulty for an archer to hit different sized circular targets.
Citing this post: Urbano, L., 2016. Some Geometry in Archery, Retrieved February 26th, 2018, from Montessori Muddle: http://MontessoriMuddle.org/ .
Attribution (Curator's Code ): Via: ᔥ Montessori Muddle; Hat tip: ↬ Montessori Muddle.
Posted in MathematicsNo Comments »  Tags: archery, geometry
April 13, 2016
3D printed volumes.
It can be tricky explaining what you mean when you say to take a function and rotate it about the xaxis to create a volume. So, I made an OpenScad program to make 3d prints of functions, including having it subtract one function from another. I also 3d printed a set of axes to mount the volumes on (and a set of crosssections of the volumes being rotated.
The picture above are the functions Mrs. C. gave her calculus class on a recent worksheet. Specifically:
from which is subtracted:
Citing this post: Urbano, L., 2016. Volumes of Revolution, Retrieved February 26th, 2018, from Montessori Muddle: http://MontessoriMuddle.org/ .
Attribution (Curator's Code ): Via: ᔥ Montessori Muddle; Hat tip: ↬ Montessori Muddle.
Posted in 3d Print, Calculus, MathematicsNo Comments »  Tags: 3d printing, calculus, volumes
February 2, 2016
Regardless, if learning is to be as efficient and deep as possible, it’s essential that it be done freely. That means giving children a voice in which activities to participate, for how long, and also the level of mastery they want to achieve. (“This is the biggest clash with traditional curriculum development,” Droujkova notes.)
— Vangelova (2014): 5YearOlds Can Learn Calculus
This article provides a lot of evidence to support the notion that the conceptual aspects of calculus and other “higher level” forms of math should be taught at all age levels, not just at the end of high school or in college.
The presentation below elaborates:
Citing this post: Urbano, L., 2016. The Joy of Math, Retrieved February 26th, 2018, from Montessori Muddle: http://MontessoriMuddle.org/ .
Attribution (Curator's Code ): Via: ᔥ Montessori Muddle; Hat tip: ↬ Montessori Muddle.
Posted in MathematicsNo Comments »  Tags: math
August 27, 2015
Toothpick shape sequences.
Using a sequence of connected shapes to introduce algebra and graphing to preAlgebra students.
Make a geometric shape–a square perhaps–out of toothpicks. Count the sides–4 for a square. Now add another square, attached to the first. You should now have 7 toothpicks. Keep adding shapes in a line and counting toothpicks. Now you can:
 make a table of shapes versus toothpicks,
 write the sequence as an algebraic expression
 graph the number of shapes versus the number of toothpicks (it should be a straight line),
 figure out that the increment of the sequence–3 for a square–is the slope of the line.
 show that the intercept of the line is when there are zero shapes.
Then I had my students set up a spreadsheet where they could enter the number of shapes and it would give the number of toothpicks needed. Writing a small program to do the same works is the next step.
Citing this post: Urbano, L., 2015. Toothpick Shapes' Sequences, Retrieved February 26th, 2018, from Montessori Muddle: http://MontessoriMuddle.org/ .
Attribution (Curator's Code ): Via: ᔥ Montessori Muddle; Hat tip: ↬ Montessori Muddle.
Posted in Algebra, MathematicsNo Comments »  Tags: geometry, math, prealgebra
March 16, 2015
The Gardening Department of our StudentRunBusiness sowed seeds in little coconut husk pellets. The question was: how many seeds should we plant per pellet.
Planting seeds in coconut pellets.
Since we’ll only let one seedling grow per pellet, and cull the rest, the more seeds we plant per pellet, the fewer plants we’ll end up with. On the other hand, the fewer seeds we plant (per pellet) the greater the chance that nothing will grow in a particular pellet, and we’ll be down a few plants as well. So we need to think about the probabilities.
Fortunately, I’d planted a some tomato seeds a couple weeks ago that we could use for a test case. Of the 30 seeds I planted, only 20 sprouted, giving a 2/3 probability that any given seed would grow:
So if we plant one seed per pellet in 10 pellets then in all probability, only two thirds will grow (that’s about 7 out of 10).
What if instead, we planted two seeds per pellet. What’s the probability that at least one will grow. This turns out to be a somewhat tricky problem–as we will see–so let’s set up a table of all the possible outcomes:
Seed 1 
Seed 2 
grow 
grow 
grow 
not grow 
not grow 
grow 
not grow 
not grow 
Now, if the probability of a seed growing is 2/3 then the probability of one not growing is 1/3:
So let’s add this to the table:
Seed 1 
Seed 2 
grow (2/3) 
grow (2/3) 
grow (2/3) 
not grow (1/3) 
not grow (1/3) 
grow (2/3) 
not grow (1/3) 
not grow (1/3) 
Now let’s combine the probabilities. Consider the probability of both seeds growing, as in the first row in the table. To calculate the chances of that happening we multiply the probabilities:
Indeed, we use the ∩ symbol to indicate “and”, so we can rewrite the previous statement as:
And we can add a new column to the table giving the probability that each row will occur by multiplying the individual probabilities:
Seed 1 
Seed 2 
And (∩) 
grow (2/3) 
grow (2/3) 
4/9 
grow (2/3) 
not grow (1/3) 
2/9 
not grow (1/3) 
grow (2/3) 
2/9 
not grow (1/3) 
not grow (1/3) 
1/9 
Notice, however, that the two middle outcomes (that one seed grows and the other fails) are identical, so we can say that the probability that only one seed grows will be the probability that the second row happens or that the third row happens:
When we “or” probabilities we add them together (and we use the symbol ∪) so:
You’ll also note that the probability that neither seed grows is equal to the probability that seed one does not grow and seed 2 does not grow:
So we can summarize our possible outcomes a bit by saying:
Outcome 
Probability 
both seeds grow 
4/9 
only one seed grows 
4/9 
neither seed grows 
1/9 
What you can see here, is that the probability that at least one seed grows is the probability that both seeds grow plus the probability that only one seed grows, which is 8/9 (we’re using the “or” operation here again).
In fact, you can calculate this probability by simply taking the opposite probability that neither seeds grow:
Generalizing a bit, we see that for any number of seeds, the probability that none will grow is the multiplication of individual probability that one seed will not grow:
Probability that no seeds will grow
Number of seeds 
Probability they wont grow 
1 
1/3 
(1/3)^{1} 
2 
(1/3)×(1/3) = 1/9 
(1/3)^{2} 
3 
(1/3)×(1/3)×(1/3) = 1/27 
(1/3)^{3} 
n 
(1/3)×(1/3)×(1/3)×… 
(1/3)^{n} 
So to summarize, the probability that at least one plant will grow, if we plant n seeds is:
which is:
Which is something we may have seen before: What are the odds?
Finally to answer our question: how many seeds we should plant, we need to decide how high a probability we need of success:
Probability that at least one seed will grow
Number of seeds 
Probability that at least one seed will grow 
% 
1 
2/3 
67% 
2 
8/9 
89% 
3 
26/27 
96% 
4 
80/81 
99% 
n 
1(1/3)^{n} 

The Head of Gardening leads the planting of seedlings.
Citing this post: Urbano, L., 2015. Planting Probabilities, Retrieved February 26th, 2018, from Montessori Muddle: http://MontessoriMuddle.org/ .
Attribution (Curator's Code ): Via: ᔥ Montessori Muddle; Hat tip: ↬ Montessori Muddle.
Posted in Mathematics, student run businessNo Comments »  Tags: probability, SRB, srb math, srb to theory
March 9, 2015
I’m having my students collect all sorts of data for Chicken Middle, their studentrunbusiness. Things like the number of eggs collected per day and the actual items purchased at the concession stand (so we don’t have to wait until we run out of snacks). It takes a little explanation to convince them that it’s important and worth doing (although I suspect they usually just give in so that I stop harassing them about). So this talk by Ben Wellington is well timed. It not goes into what can be done with data analysis, but also how hard it is to get the data in a format that can be analyzed.
Doubly fortunately, Ms. Furhman just approached me about using the Chicken Middle data in her preAlgebra class’ chapter on statistics.
We’re also starting to do quarterly reports, so during this next quarter we’ll begin to see a lot of the fruits of our datacollecting labors.
Citing this post: Urbano, L., 2015. The Importance of Collecting (and Reporting) Good Data, Retrieved February 26th, 2018, from Montessori Muddle: http://MontessoriMuddle.org/ .
Attribution (Curator's Code ): Via: ᔥ Montessori Muddle; Hat tip: ↬ Montessori Muddle.
Posted in Experiential, Mathematics, student run businessNo Comments »  Tags: data analysis, student run business
September 2, 2014
Mike Schmidt passed along this link to Lisa Winter’s post collecting 21 GIFs That Explain Mathematical Concepts.
For example:
Citing this post: Urbano, L., 2014. Math Gifs, Retrieved February 26th, 2018, from Montessori Muddle: http://MontessoriMuddle.org/ .
Attribution (Curator's Code ): Via: ᔥ Montessori Muddle; Hat tip: ↬ Montessori Muddle.
Posted in MathematicsNo Comments »  Tags: animations, math, preCalculus