Although the explanation are simple and direct,they challenge students to think. When asked to find the difference between 9 and 6 ,for example,students understand that they need to use subtraction because of the part-whole relationship that has been used to teach them addition and subtraction.Because they know that 6 is part of 9 , they easily understand how to find the difference. Practice problems in Singapore Math are designed to teach skills step by stap. The first few practice problems in a typical lesson might provide the appropriate bar model,whereas succeeding problems require the student to construct it.