We have just published another set of worksheets which looks at adding three small numbers mentally. As usual the questions are very specific, concentrating on the concepts needed to complete these as quickly as possible. In this case two of the three numbers will add up to exactly 20, leaving just the third number to add on. Of course, children do need to know that addition can be done in any order and they do need to know the pairs of numbers that make 20 (e.g. 19 and 1, 18 and 2 etc.) Go to More Addition of Three Numbers