Yellow Door Number Pebbles - Sum Building SetProduct Description: Get hands on with sums. These tough, tactile pebbles are cast from a unique and durable mix making them suitable for use across a setting including outdoors. Great for learning and practising addition and subtraction to 20 (including zero), problem solving and creating mathematical statements, they are a flexible and engaging numeracy resource. Each set includes two each of umbers 0 20, +, , = and one each of x and (50 pebbles).