If Pie Charts are too confusing (as they may seem like 2 separate diagrams), try bar models. It is easier to compare by using their lengths. Primary 4 students should have a strong grasp on the concept of 1 whole etc. Hence, only need to explain how /3 can be converted to /6 (simply by cutting each of the 3 parts into halves). Of course, after all that, need to clarify how to extract the final answer from the diagram (can use cancel or shade to eliminate).