Dear Uncle Colin,

When evaluating an expression, after you’ve dealt with brackets, powers and roots, do you deal with multiplication and division left to right, or does multiplication take precedence?

- BIDMAS Idiocy Doesn’t Make Any Sense

Hi, BIDMAS, and thanks for your message!

There are three answers to this.

If you’re a computer, you evaluate operators of the same precedence - such as multiplication and divide - from left to right, by convention.

If you’re a human, you try to figure out from the context what the person writing the expression meant, regardless of BIDMAS. Someone on Reddit might write 1 / x-3 to mean $\frac{1}{x-3}$ rather than the $\frac{1}{x} - 3$ a strict interpretation of the rules gives.

And if the question is $6 \div 2(1+2)$, you say “This is fake maths, write the bloody thing properly.”

Hope that helps!

- Uncle Colin