Consumable. “Extra” word problems–and only word problems–to help your child master the concepts or to provide him or her with more challenge than is contained in the same numbered Singapore Primary Math (U.S. Ed.) book. Problems are arranged by topic, though not always in the same order as found in the Primary Math Series. Answers are provided at the end of each book. These texts are challenging, especially by the time you get to the Primary 4 level.