Key Actions Of The Nine-dot Problem Solving

Past researches indicated that, the nine-dot problem, one of the classical insight problems, was hard to solve. But the key action to solve the nine-dot problem has not been found. So we hypothesized that drawing out the third line was the key action to solve the nine-dot problem. There were three experiments to verify the hypothesis. We researched 330 undergraduates individually. After the students who couldn't solve the nine-dot problem had done the training problem, we let them solve the nine-dot problem again to get the solution rate of the nine-dot problem. The results of experiment 1 indicated that the solution rate was close to or reach 100% after we clued subjects to any two lines at the same time, Clues of two lines were "over clues", they weren't the key actions to solve the nine-dot problem. The results of experiment 2 indicated that the solution rate was significantly higher after we clued subjects to the third line than after cluing subjects to any of the other line alone, drawing out the third line was the key action to solve the nine-dot problem. The results of experiment 3 indicated the trainings that lead subjects to draw out the third line (e.g. "five-dot training" and "seven-dot training") were helpful to solve the nine-dot problem. The effect of these trainings was significant While, the trainings that made subjects against to draw out the third line (e.g. "eleven-dot training" and "twelve-dot training") were not significantly helpful to solve the nine-dot problem.