Three solutions above the dam

Because the homonym of the dam is 8, both the upper and lower parts of the dam are 8, that is, 7 and 9, so the number is 789.

The earliest tools used by human beings to count are fingers and toes, but they can only represent numbers within 20. When the number was large, primitive people mostly counted pebbles and beans. Gradually, people were not satisfied with counting by grains, so they invented the method of knotting to describe counting, and described counting on hides, bones, trees and stones. In ancient China, counting was done with sticks made of wood, bamboo or bones, which was called counting chip. These counting methods and symbols gradually became the earliest digital symbols (numbers). Today, all countries in the world use Arabic numerals as standard numbers.

Around 500 AD, with the rise and development of economy, culture and Buddhism, Punjab in the northwest of Indian subcontinent has been in a leading position in mathematics. Astronomer Ayepihite made a new breakthrough in simplifying numbers: he recorded the numbers with a grid. If there is a symbol in the first grid, such as a point representing 1, then the same point in the second grid represents ten, and the point in the third grid represents one hundred. In this way, not only the digital symbols themselves, but also their position order is of great significance. Later, Indian scholars introduced the symbol zero. It can be said that these symbols and representations are the old ancestors of Arabic numerals today.