The aim of this study is to enable pupils to use forward inferences and choose an appropriate operation by reading problem statements and understanding two quantities which are dependently related. During the practice, pupils were encouraged to find out and extract the necessary quantity and decide which operation to use in each situation. As a result, pupils learned to judge whether the answer concerns global or local; in other words, paying attention to interdependent quantities made it possible to have a forward inference and choose an appropriate operation in calculation. Moreover, having a forward inference enables pupils to draw figures voluntarily and come up with formula. Eventually, they learned to understand the importance of relating all the sources, such as formula, figures and problem statements to solve the problems through practice to consider the meaning of formula.