In the adaptive assessment heuristic framework, a problem is selected to maximize the student's knowledge acquisition. This is formulated as: $s^{*} = argmax [p_sn_s^+ + (1-p_s)n_s^-]$ Here, $p_s$ is the probability that the user will solve problem $s$, $n_s^+$ is the number of problems the user can solve correctly, and $n_s^-$ is the number of problems the user cannot solve. The probability $p_s$ is estimated by: $p_s = \frac {N^+} {N^+ + N^-}$