# Workshop on Pascal's Triangle for Middle School Students

We're going to hold a three-hour math workshop for some middle school students. It'll about the Pascal's triangle.

Well, we can ask the students to find patterns in the triangle, or try to prove some of its easiest properties. But on the one hand they'll soon get to properties which are not easy enough to be left to them to be proved, and on the other hand we want the workshop to be fun and exciting.

So we need

• Some activities (building something, a game) related to the triangle,
• An interesting short movie about the triangle,
• Some tasks about the triangles to be given to the students to do , on their own.

I'd be grateful if you could share your ideas with me, and help me with finding what is needed (namely, the items above).

P.S. These are some of interesting properties of the triangle, which are not likely to be easy to be proved by the students on their own:

• The rows are symmetric.
• Each element is the sum of the two elements above it.
• Elements of each row sum up to a power of 2.
• Elements in a row related to a prime number are all divisible by it - except the two 1's.
• what exactly are you asking for? – YYC Sep 30 '13 at 15:13
• Couldn't I make myself clear? Well, maybe I should edit the post! I'm asking for 1) ideas to be used in the workshops, and 2) help with finding the items mentioned above to be needed. – Behzad Sep 30 '13 at 15:17
• Vi hart has some interesting ideas, and this may work as your short movie. khanacademy.org/math/recreational-math/vi-hart/doodling-in-math/… – Trurl Sep 30 '13 at 15:31
• if you mark the numbers which are even, you'll get a nice pattern – user8268 Sep 30 '13 at 17:01
• @Trurl: That is absolutely hilarious. – Brian M. Scott Sep 30 '13 at 23:02

A property that combines two interesting kinds of number:

$$\newcommand\br{\color{brown}}\begin{array}{cc} &&1\\ &\swarrow&\br{1}&1\\ 1&\swarrow&1&\br{2}&1\\ \br{1}&\swarrow&\br{1}&3&\br{3}&1\\ 2&\swarrow&1&\br{4}&6&\br{4}&1\\ \br{3}&\swarrow&\br{1}&5&\br{10}&10&\br{5}&1\\ 5&\swarrow&1&\br{6}&15&\br{20}&15&\br{6}&1\\ \br{8}&\swarrow&\br{1}&7&\br{21}&35&\br{35}&21&\br{7}&1\\ 13&\swarrow\\ \br{21} \end{array}$$

The diagonal sums are the consecutive Fibonacci numbers. (The fact isn’t even all that hard to explain informally: the construction rule for Pascal’s triangle naturally produces the Fibonacci recurrence.)

There are the hockey stick (or Christmas stocking) patterns:

$$\begin{array}{cc} \begin{array}{cc} x\\x\\x\\\vdots\\x\\x\\&\searrow\\ &&\text{sum} \end{array}&\quad&\text{and}&\quad&\begin{array}{cc} x\\&x\\&&x\\&&&\ddots\\&&&&x\\&&&&&x\\&&&&&\downarrow\\&&&&&\text{sum} \end{array} \end{array}$$

Reducing Pascal’s triangle mod $2$ produces the Sierpiński triangle, which has all sorts of patterns:

$$\newcommand\0{\color{magenta}0}\begin{array}{r|cc} \underline{0}&\underline{1}\\ \underline{1}&\underline{1}&\underline{1}\\ 2&1&\0&1\\ \underline{3}&\underline{1}&\underline{1}&\underline{1}&\underline{1}\\ 4&1&\0&\0&\0&1\\ 5&1&1&\0&\0&1&1\\ 6&1&\0&1&\0&1&\0&1\\ \underline{7}&\underline{1}&\underline{1}&\underline{1}&\underline{1}&\underline{1}&\underline{1}&\underline{1}&\underline{1}\\ 8&1&\0&\0&\0&\0&\0&\0&\0&1\\ 9&1&1&\0&\0&\0&\0&\0&\0&1&1\\ 10&1&\0&1&\0&\0&\0&\0&\0&1&\0&1\\ 11&1&1&1&1&\0&\0&\0&\0&1&1&1&1\\ 12&1&\0&\0&\0&1&\0&\0&\0&1&\0&\0&\0&1\\ 13&1&1&\0&\0&1&1&\0&\0&1&1&\0&\0&1&1\\ 14&1&\0&1&\0&1&\0&1&\0&1&\0&1&\0&1&\0&1\\ \underline{15}&\underline{1}&\underline{1}&\underline{1}&\underline{1}&\underline{1}&\underline{1}&\underline{1}&\underline{1}&\underline{1}&\underline{1}&\underline{1}&\underline{1}&\underline{1}&\underline{1}&\underline{1}&\underline{1}\\ \end{array}$$