300-246 equals 54. Mathematical subtraction is one of baby penguin's favorite series. "Mathematical Subtraction" is a children's book, which was secretly written by China Children's Intelligence Development Editorial Room to teach children some basic knowledge. Children aged 0 ~ 6 months will stare at the items pointed by adults after reading them. 7 ~ 12 months can pick out the learned cards according to the instructions of adults. 13 ~1August can recognize squares, circles and triangles. I like to draw with colored pens. /kloc-from 0/9 to 24 months, you can know more than three natural phenomena and tell the uses of more than four items.