The abacus in the inquire-based learning of addition and subtraction
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Salvador, v. 5, n. 2, p. 22-39, mai./ago. 2020
fortunately, generally come with different colors, which may induce the student to correlate color
and value for the pieces. It is an important that the teacher uses this situation of error to emphasize
that all the round pieces are identical and use them interchangeably in the sticks. The teacher can
then stress the difference between numbers and digits (“algarismos” in Portuguese), which can be
quite fuzzy for many students.
These two activities are made to stress the issue of number representation. At rst, only
the rst three numeric places are mentioned (the place/stick representing the units digit, the one
representing the tens digit and the one representing the hundreds digit). They are then asked (rst
problem) to generalize this representation by saying what the fourth stick in the abacus should
represent. To end this activity about representation, the teacher then explains the students the impor-
tance of having a decimal representation, by showing that without it, if each new piece represents
the successor number, to count up to nine thousands would mean to pile up nine thousand pieces
– in a structure bigger than the classroom –, while in the decimal representation it would mean
to just use nine pieces of wood (this point generally raises much astonishment). The teacher then
asks the students to join into groups (of no more than four or ve students) and, after the groups
are made, he asks them to represent a small list of numbers, just to make them as much acquainted
with the abacus as possible. The teacher must stress that, as with the human abacus, each stick can
hold at most ten pieces of wood, like it happened with each student in the “human abacus”. These
two rst activities should take no more than one class of 50 minutes. If the students show easiness
to pass these activities, the teacher can then present the notation of numbers using classes and
orders, and the use of the comma to make them explicit in number representation. At this stage,
students frequently nd quite amusing to work with very large numbers, such as 1,323,897,765
even if only to utter them;
Activity 3
The next activity introduces number addition. There are a number of details that should be
taken into account when teaching this operation. Details at this level of teaching are very important
and should not be overlooked by the teacher – moreover, they must be made explicit to the students.
The teacher begins asking the students to represent in the abacus some number, for example 143,
and then asks them to add this number with the number 2 (no student presents any difculty to do
that). The teacher may ask them to add another number that does not surpass 10, just for xation.