## Powers of 2

This is a really quick method I've found for estimating what 2^n is. As we can see on the left there is some kind of pattern as to when we move up an order of magnitude If your n ends in a 0 a 4 or a 7 then you will be on the first… Continue reading Powers of 2

## Compounding

Before getting to the general rules I've come up with lets take a quick look at the most famous method to solve compounding questions. The rule of 72: what is it and why does it work "In order to find the time it takes to double your money divide 72 by the rate of return"… Continue reading Compounding

## Sample size

When we see an economic study or scientific test how do we know if the results are reliable? How do we know if we should pay attention to what we see labelled as scientific? We can look at the methodology or the ways the data was analysed but there is one thing that can act… Continue reading Sample size

## Approximate geometric means

This post relates to finding the mean of two numbers. If I asked what the mean of 3 and 27 most people would say it was 15 but this is simply one version of the mean, the arithmetic mean (AM), where we look for a number that is an equal distance from the two through… Continue reading Approximate geometric means

## Square roots

How can you figure out the square root of a number quickly and to a decent degree of accuracy. You can try and figure out which squares the number falls between and try to guess where it falls but how can you do that accurately? Some of you will have heard of a Taylor series.… Continue reading Square roots

## Mental maths: Logarithms

What is ln(8)? What about ln(100)? Or how about log2(10)? Logarithms can help us solve questions involving exponentials or cumulative events and, whilst you will rarely have to solve them without a calculator, I think being able to is a fun trick to know. To be able to solve any logarithm you need to know… Continue reading Mental maths: Logarithms

## Mental maths

This is introducing a series on useful mental maths that I think it dramatically helps to know. It's true that in many professions being able to carry out complicated maths isn't required, however, it's also true that having some level of numeracy will help in almost all walks of life. I'm going to try and… Continue reading Mental maths

## Kelly criterion

I first came across the Kelly criterion in a paper by Haghani & Dewey where they give contestants a coin with a 60% chance to show heads, £25 and 300 flips to maximise their money. Well when I first read the question my performance would have likely been about as good as the average player,… Continue reading Kelly criterion