## Archive for December 9, 2014

### Mental Math and the MCWC

How long would it take you to find the sum of 2 two-digit numbers?

What about 3 three-digit numbers?

Or 4 four-digit numbers?

Okay, let’s get really crazy… how long would it take you to find the sum of 10 ten-digit numbers?

You can decide whether you’ll do the calculation in your head, on a calculator, or with paper and pencil. Your choice.

With a calculator, it took me 91 seconds to find the sum of 10 ten-digit numbers.

Without a calculator, the winner of the Mental Calculation World Cup 2014 needed only 242 seconds to complete 10 problems in which participants were asked to add 10 ten-digit numbers. On average, that’s just 24 seconds to do in his head what took me a minute-and-a-half with technology.

Holy smokes!

Competitors at the MCWC do a number of mental calculation tasks. The following exercises will give you an idea of the computations that they do.

Exercise 1. Sum of 10 ten-digit numbers.

$\begin{array}{r} \mathbf{4190187220}\\ \mathbf{3967093178}\\ \mathbf{8567125486}\\ \mathbf{1005683165}\\ \mathbf{3635944647}\\ \mathbf{7645865467}\\ \mathbf{3506970235}\\ \mathbf{6710259450}\\ \mathbf{2 347 894 647}\\ \mathbf{\underline{ + 4 995 420 559}}\\ \end{array}$

Exercise 2. Multiplication of 2 eight-digit numbers.

$\begin{array}{r} \mathbf{18467941}\\ \mathbf{\underline{ \times 73465135}} \end{array}$

Exercise 3. Square root of a six-digit number.

$\mathbf{\sqrt{530179}}$

Exercise 4. Day of the week for a calendar date.

$\textbf{8 December 1721}$

Exercise 5. Multiplication of 3 three-digit numbers.

$\mathbf{184 \times 734 \times 635}$

These sample exercises are taken from the examples in the MCWC 2014 Official Rules.

If you were able to complete all five of those exercises in, say, less than 3 minutes, then you might be ready for MCWC 2016. (Note that for Exercise 3, you needed to be accurate to within 5 × 10-6.)

But if you’re like me, you’ll probably want to skip the competition and keep your calculator close at hand.

The Math Jokes 4 Mathy Folks blog is an online extension to the book Math Jokes 4 Mathy Folks. The blog contains jokes submitted by readers, new jokes discovered by the author, details about speaking appearances and workshops, and other random bits of information that might be interesting to the strange folks who like math jokes.

## MJ4MF (offline version)

Math Jokes 4 Mathy Folks is available from Amazon, Borders, Barnes & Noble, NCTM, Robert D. Reed Publishers, and other purveyors of exceptional literature.