The purpose of these procedures is to change the initialnumbers of the calculation into different ones with whichcalculating is easier (Gomez, 1989). For example, if we hadto calculate 35 þ 29, one option would be to round up 29 to30, and then add the remaining 34. In contrast, if the addition were 34 þ 23, rounding up to the nearest 10 wouldprobably not be the most effective strategy. In this case,most likely decomposing both numbers into tens and units,before adding them up would be a more efficient approach:(30 þ 4) þ (20 þ 3) ¼ (30 þ 20) þ (4 þ 3) ¼ 50 þ 7 ¼ 57. Someauthors refer to this as reflexive or thought calculation(Gomez, 1989) to emphasize the difference with more mechanical computation such as the rapid recall of basic numberfacts (Department for Education, 2010).