You can do many things with mathematical knowledge in your life. For example, you can calculate some addition, subtraction, multiplication and division, and you can buy food and go to the supermarket. And you can estimate the data according to the actual situation. For example, you can calculate the travel time by knowing the distance and speed. For example, if you know the length and width of a house, you can calculate the approximate area of the house. For example, when you do experiments, you can calculate the current and power by knowing the voltage and resistance. The list goes on and on.