## 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.

**Exercise 2.** Multiplication of 2 eight-digit numbers.

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

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

**Exercise 5.** Multiplication of 3 three-digit numbers.

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.