A pretty straightforward worksheet in two parts. The first part looks at subtraction of a single digit from multiples of 100. The second half looks at subtracting from multiples of 1000. The obvious way to do this is to count back, but when you ask children who are very quick with maths they seem to employ other tactics with little to do with subtraction. For example, one 9 year old boy told me his explanation of 8000 – 6:
‘turn the 800 into 799 and add 4 to make the next whole ten. Answer 7994’
Not the clearest explanation ever, but it seems that he is doing a kind of decomposition in his head – interesting!