median
don steward
mathematics teaching 10 ~ 16

## Saturday, 31 August 2019

### bidmas differences

one of the reasons why some people do not like to use the mnemonic 'bidmas' (or 'pemdas') is that it can lead to some students misguidedly working out division prior to multiplication (or vice versus for pemdas) and an addition prior to a subtraction

it ought perhaps to be labelled:

but this doesn't ensure a lack of confusion

Matt Dunbar has suggested using this graphic:

it seems to be important that students have some notion of a more 'powerful' operation
as well as a need for a global convention, to avoid ambiguity

it can be interesting to look at the difference between a calculation worked out (a) using a correct priority of operations and (b) incorrectly

there are three tasks here, looking at these differences for:

1.  3 consecutive numbers
2.  where the first number is 10 times the second and the third is the second add 1
3.  where one result (incorrect version) is double that of the other (correct version)

a powerpoint is here

diagrams of the different ways that this can be worked out

as can be seen in the diagram above

as can be seen in the diagram

examples where one (incorrect) result is double the correct result