Subtracting numbers either side of a hundreds boundary is often most easily done by counting up.
Working with numbers either side of the thousands boundaries. Easier done 'in your head' than on paper.
Good practice at counting down, crossing the thousands boundary. Don't forget the 'help' link on the top right which shows a way of tackling these types of questions.
The best way to do these is to subtract the nearest multiple of ten and then adjust the answer.
Subtracting a decimal from a 2-digit number 'in your head'. Often best done by 'adding on'. Only one minute to answer as many as possible, but don't expect a high score: anything over ten would be really good.