Math Magic or Calculators?

I was perusing my news feed trying to find something of interest to write about, and came across an article entitled “The Common High School Tool That is Banned in College” i.e. the calculator. It’s an interesting article, worth a read,  basically comparing the high school perspective on the use of calculators to the college perspective or non-use of calculators. There is no right or wrong answer – I think it depends on the math content, what you want students to do (i.e. basic algorithms to solve problems or using mathematics to solve deeper problems).  Depending on your goals, the use of calculators and technology differs. As with any technology, calculators are a resource that needs to be used appropriately, and we need to be teaching that.  Common Core Mathematical Practice #5 – Using Appropriate Tools Strategically is all about this. Calculators have their place and are important to help explore and expand mathematical understanding, but we have to help students understand when their use is necessary and not a ‘crutch’, as stated in the article.

This was on my mind obviously, when I then ran across a tweet post by Go!Math Videos @gomathvideos that shared a TedX talk by Arthur Benjamin entitled “Faster than a Calculator”, which naturally sparked my interest and seemed related to the question of should we be using calculators. In the video, Arthur Benjamin has members of the audience use calculators while he does calculations in his head. He then goes on to wow everyone with his math ‘tricks’ (what he calls mathemagics). He ends by doing a 5-digit square calculation by thinking out loud as he ‘solves’ a problem. It’s fascinating – he changes numbers to words to help him solve – he is definitely using his own ‘algorithm’. The video does not answer the question should we be using calculators – but it definitely shows that calculators are just one way to get a solution and it may not always be the fastest. Anyway – just some fun for this last post of 2016. Enjoy!

Wishing everyone a Happy and Safe New Years!

A Partridge In a Pear-Tree – How Many Presents?

As it is the holiday season and most people are out of school and busy getting ready for family celebrations, shopping, and whatever other holiday customs might be of importance to you, I thought it might be fun to look at the math behind a popular Christmas song that I know all of you have been hearing (since Thanksgiving) whenever you walk into any store.

I realize that many of you may not celebrate Christmas –  I myself celebrate both Christmas and Hanukkah, so my family has several different traditions. I realize there are many of you out there with your own traditions and customs during this winter break (i.e. Christmas, Hanukkah, Kwanzaa, to name a few). That’s the beauty of this country – you can celebrate and enjoy your own traditions. My focus is as always on math and/or technology, and I happened to find this interesting YouTube video that incorporates Pascal’s Triangle into a very popular Christmas song – The 12 Days of Christmas. Even if you don’t celebrate Christmas, you know you have heard this song (I believe I have been stuck on the elevator more than a couple times with this song being piped through)! Hopefully you will enjoy the math aspect of this and next time you hear the song in the stores you can share the math calculations with fellow shoppers.

How many presents is that? Pascals Triangle can help!

We at Casio wish all of you Happy Holidays whatever you may be doing or celebrating!


The Last Five Minutes of Class

You teachers out there know that those last five minutes of class – when students are ‘packing up’ even if you are not quite finished with the class activities, or, you’ve finished and they are suppose to be working on their assignments or reviewing – are often  a ‘wasted’ five minutes. In my many years at schools, I saw teachers use that time in various ways – but more often than not, it was simply time to get ready to leave, basically chat time and get your stuff together and wait time. Not productive learning time at all.

It’s easy enough to make these moments into fun, engaging, mathematics problem-solving that students, believe it or not, actually come to enjoy and request. I use to have a few different things that I would pull out – focusing on either logical thinking or number-sense or puzzles. Here are just a couple of things:

  1. I had the 24-game – several different versions.  I(If you have never played this or seen this, you should explore it). So, in those last 5 minutes, I would pull out a card, write the 4 numbers on the board and students would try to reach the target of 24. As an example: 2, 3, 4, 4 and you can add, subtract, multiply or divide using each number one time, to make 24. I often had candy for anyone who could come up with a strategy.
  2. If you don’t have actual cards, you can create your own version of ‘reach the target’.  So, pick 4 random numbers using a calculator, and give students a target number to try to reach (so 24). Or, choose 2, 3, or 4 random numbers with a calculator (or have students give you numbers) and ask students to use all the operations and come up with the smallest outcome and/or the largest outcome.  This is a lot of fun – you get some interesting problems and students have to explain their answers and defend their solutions.
  3. Give the students a logic puzzle.  I actually purchased several logic books, and so would read one out to the students or draw/show the picture on the screen and they could work in pairs/small groups to try to come up with a solution. Great critical thinking and collaboration going on here – and if we couldn’t get the solution before the bell rang, we would take it up the next day with most of them working on it overnight. Here are some good resources for logic puzzles:
  4. Read a story.  Yep. Even with my high school students, I would read stories.  Math related of course. You would be amazed at how they actually enjoyed listening, and of course, once the ‘story’ was finished (which might take a couple days depending on our actual time at the end of each class) we’d discuss the ‘math’. Some of my favorite books:

Students loved the challenge of these last 5 minutes (sometimes it would be more). It was a very competitive yet non-threatening time where they could test their math skills or thinking skills, work together, and have fun with numbers and logic. That time was no longer wasted – it became a time students actually looked forward to and often requested.

As you are nearing the winter break, there is probably a bit more time to spare or a bit more time needed to keep students attention.  Use that time in an engaging way that allows for some critical thinking, collaboration and a game-like atmosphere that challenges students and keeps those last five minutes productive.

Permutations & Combinations – Casio vs. TI

img_3628I share a twin house with my neighbors (i.e. we are attached) and we like to decorate our front porches for the holidays the same, so that our ‘house’ is coordinated.  Every year we do something different, and this year we decided to hang holiday ornaments along with the lights – so a variety of Christmas balls and various large ornaments hanging from the porch.  As we were trying to decide the most ‘pleasing’ order to hang these, I realized we were basically discussing combinations and permutations, which naturally got me thinking about working with this in math class.

Permutations and combinations are often very confusing for students. Basically you have a group of things (numbers, objects) and you are going to pick a certain amount from that group of things, and depending on whether order matters, you either have a certain number of combinations of things you can make or a certain number of permutations. Combinations are the possibilities of things chosen when order doesn’t matter. Permutations are the possibilities of things chosen when order does matter.

As an example:


We have 3 Christmas Balls – green, red, blue.  If I want to choose two, order doesn’t matter, than it’s a combination, so how many combinations will I get?

3 combinations: Green, Red;  Green, Blue; or Red, Blue

But, if order does matter, then we have a permutation, so how many permutations are there?

6 permutations: Green, Red; Red, Green; Green, Blue; Blue Green; Red, Blue; Blue, Red.

Now, there’s also the whole idea of replacement and no replacement, but I am not going to get into that here. Working with students, you would want to start with small numbers of objects so they can create the combinations and permutations by hand. But then, you’d want to lead into more complicated things such as lottery numbers and chances of winning, where finding all the combinations and/or permutations is hard to do by hand, thus requiring a formula to make it more efficient, and then eventually, if you really want to do comparisons and have interesting discussions about many real-world examples, you’d want to incorporate technology to help be even more efficient. Here’s a nice page I found that discusses the differences between combinations and permutations and the different formulas needed and provides some good examples.

Below is how you can calculate permutations and combinations when you know your sample size (n = number of things you have) and how many you are choosing (r) from that group of n things. This video shows how to do this on both the Casio Prizm and the TI-84+CE.

Clearly in my front-porch, neighbor decision making, order actually mattered. We wanted a pleasing arrangement. We therefore were looking for permutations – how to choose six balls from a possible 10, so 10P6. There are a staggering number of permutations – 151,200.  Who knew holiday decorating had so many choices!!!  Needless to say we did not try to look at all of them – but good to know we have so many options for the years to come!