# Browsing category ninja maths

## Secrets of the mathematical ninja: some numbers worth knowing

Learning the rough value of a few key numbers worth knowing can make ninja maths a lot more impressive later on - especially if you know how roughly how rough the rough values are. A little bit about the tables below: I'm giving you decimals to two sig figs, the

## Secrets of the Mathematical Ninja: The surprising integration rule you don’t get taught in school

Difficulty: ** Impressiveness: **** If you do A-level maths, you do an awful lot of integration. You integrate polynomials, trig functions, partial fractions, exponentials, parametric curves, products of these... and get nice analytical answers. Here, let me provoke controversy: Unless you're going to be a pure mathematician or a maths

## Secrets of the Mathematical Ninja: powers near 1

Difficulty: (simple version) *** (advanced version) ***** Impressiveness: ***** Accuracy: *** If you're a statistician, you quite often end up working out powers of numbers just a little less than 1. What's the probability of rolling a pair of dice ten times and never getting a double six? It's $\left(\frac{35}{36}\right)^{10}$.

## Secrets of the mathematical ninja: Divisibility tricks

Some of the secrets of the mathematical ninja are pretty pointless, when you come down to it: after all, we have machines for most of these things. The divisibility tricks are useful (as far as I can see) only in a very specific circumstance: when you're deciding whether to cancel

## Secrets of the Mathematical Ninja: squares near 50.

Difficulty: ** Impressiveness: **** (Many thanks to Swar for pointing me at this one - and challenging me to explain it well!) It's surprisingly easy to square numbers near 50. Here's the recipe: 1. Find the difference between your number and 50. (If you're looking at 46, it'd be -4.

## Squaring halves (and fives): Mathematical Ninja Secrets

The trick: someone says 'what's 7.5 squared?' and - mentally squaring in a flash - you say: 56.25. Squaring halves Squaring halves is really easy if you know your times tables. Here's the method: Take your number and find the whole numbers immediately above and below. If you're trying to