1、Engraved Symbols: The symbols on the surface of the dices are engraved, so the minus and plus symbols on the dices will not be worn even after long term use. 2、Plastic Material: These math operation dices are made of premium plastic material, which is not easy to be damaged and can be used for a long time. 3、Development of Intelligence: These math calculation dices are applicable to infant education and has a helping role in developing children's intelligence. 4、Attention Attracting: The math dice set adopts dice shape design, which can well attract children's attention and let them participate in mathematical operations. 5、A Perfect Toy: This plus minus dice set can be used as a perfect toy for children. While entertaining, children can also learn some mathematical knowledge. Item Type: Plus minus dice set Material: Plastic Weight: Approx. 80g/2.8oz Product Size: 1.6x1.6x1.6cm/0.6x0.6x0.6in Applicable: Mathematics teaching 20 x Dice