Readable By All (Posts about mental math)http://drwxr-xr-x.org/enContents © 2021 <a href="mailto:n.tesla@example.com">Dylan Leigh</a> Mon, 18 Oct 2021 20:13:29 GMTNikola (getnikola.com)http://blogs.law.harvard.edu/tech/rss- Sunday Maths: The Diagonal-Sum Mental Multiplication Methodhttp://drwxr-xr-x.org/posts/2019/11/sunday-maths-the-diagonal-sum-mental-multiplication-method/Dylan Leigh<div><p>This is a mental math technique to solve non-trivial integer
multiplication I picked up from one of Arthur Benjamin's talks, and is
widely used by other "mathemagicians" to solve large products.</p>
<p>It converts an n × n multiplication problem into a n² set of single
digit multiplications, arithmetically identical to the <a class="reference external" href="http://mathworld.wolfram.com/LatticeMethod.html">"Lattice
Method"</a>. However,
instead of filling the lattice first and then summing each diagonal,
this method calculates each sum as soon as possible - thus you only
need to keep track of the bare minimum of working data and it becomes
possible to do the problem entirely in your head.</p>
<p><a href="http://drwxr-xr-x.org/posts/2019/11/sunday-maths-the-diagonal-sum-mental-multiplication-method/">Read more…</a> (4 min remaining to read)</p></div>algebraarithmeticcombinatoricsmathematicsmental mathsciencehttp://drwxr-xr-x.org/posts/2019/11/sunday-maths-the-diagonal-sum-mental-multiplication-method/Sun, 24 Nov 2019 05:34:18 GMT
- Sunday Maths - Quickly Multiplying Teenshttp://drwxr-xr-x.org/posts/2019/11/sunday-maths-quickly-multiplying-teens/Dylan Leigh<div><p>In a similar vein to <a class="reference external" href="http://drwxr-xr-x.org/posts/2019/11/sunday-maths-simplifying-squares/">last week's post on simplifying squares</a>, this one uses some basic
algebra to make it easier to multiply numbers between 10-20:</p>
<pre class="literal-block">
(10 + x)(10 + y) = 100 + 10x + 10y + xy = 10(x + y + 10) + xy
</pre>
<p><a href="http://drwxr-xr-x.org/posts/2019/11/sunday-maths-quickly-multiplying-teens/">Read more…</a> (1 min remaining to read)</p></div>algebraarithmeticcombinatoricsmathematicsmental mathsciencehttp://drwxr-xr-x.org/posts/2019/11/sunday-maths-quickly-multiplying-teens/Sat, 09 Nov 2019 14:47:05 GMT
- Sunday Maths: Simplifying Squareshttp://drwxr-xr-x.org/posts/2019/11/sunday-maths-simplifying-squares/Dylan Leigh<div><p>This is a simple method to make it easier to calculate squares in your
head (or on paper). The key is the following equation:</p>
<pre class="literal-block">
x² = (x+y)(x-y) + y²
</pre>
<p><a href="http://drwxr-xr-x.org/posts/2019/11/sunday-maths-simplifying-squares/">Read more…</a> (1 min remaining to read)</p></div>algebraarithmeticcombinatoricsmathematicsmental mathsciencehttp://drwxr-xr-x.org/posts/2019/11/sunday-maths-simplifying-squares/Sun, 03 Nov 2019 04:49:23 GMT