A particular type of subtraction question seems to cause more problems than almost any other kind, and that is where a ten needs to be 'borrowed' from the tens column but there is a zero in the tens. In this case the adjustment needs to be done from the hundreds to the tens and then from the tens to the units. There is an explanation page at the start of this set of worksheets. There are two main areas of difficulty. Watch out for the common error of jumping straight from the hundreds to the units; this makes the the number 100 less but the adjustment only 10 more, so the final calculation will be 90 less than it should be. Another common error that children make is to say that zero subtract three is 3. This of course makes the calculation easier as there is no adjusting to do, but will result in an incorrect answer!