Building on the work done on subtraction in Year 3 the next step is to subtract up to 4-digit numbers, including exchanges. Base 10 and place value counters provide really useful visual guides as to what happens when we subtract with exchanges. We have just published 3 new sets of pages on this topic to help with subtracting two 4-digit numbers. The exchange could take place from the tens, hundreds or thousands. When doing these, children might make the mistake of finding the difference between the two digits in a column rather than subtracting the second digit from the first, or top, digit.