BIDMAS 7
"Christmas Stocking" calculators cannot do BIDMAS!
4 + 6 x 2 - 5
multiply first: 4 + 12 - 5
add next: 16 - 5
subtract: 11
Cheap calculators will do 4 + 6 first and end up with 15
Now you need to practise:
downloadable worksheet
(save this file then run it)