  This paper shows the results of an experiment applied to 170 students from
two Chilean universities who solve a task about reading a graph of an affine
function in an online assessment environment where the parameters (coefficients
of the graphed affine function) are randomly defined from an ad-hoc algorithm,
with automatic correction and automatic feedback. We distinguish two versions:
one of them with integer coefficients and the other one with decimal
coefficients in the affine function. We observed that the nature of the
coefficients impacts the mathematical work used by the students, where we again
focus on two of them: by direct estimation from the graph or by calculating the
equation of the line. On the other hand, a feedback oriented towards the
"estimation" strategy influences the mathematical work used by the students,
even though a non-negligible group persists in the "calculating" strategy,
which is partly explained by the perception of each of the strategies.
