Computers have not quite taken over the world, but many people rely on them. They forget that behind all the computing power is a mathematics system that must be learned by those who create programs, but it is often left out of the information people are given about their devices. The goal of programming is to make it user friendly, and it is considered boring to inform them of the many steps necessary to create the look of intelligence in their machines.
Advanced mathematics is taught in many public schools, but few students enjoy it. They see it as a series of classes they must master, and many of them forget it as soon as they graduate. Fortunately, mathematics is a progressive system, and students must retain the knowledge they learned earlier to pass future classes. It reinforces what they have learned previously, and forgetting it means they cannot move on to advanced classes.
There are not many fields where advanced mathematics is done by hand, but knowing how to work formulas without a computer is often expected. Calculators and other devices are often forbidden for student use, so it is a way to help them learn to do it without electronic assistance. They may never use it in the real world, but it is always good to know they can do it without a machine if the batteries go dead. Navigating without electronics might seem impossible, but just a few basic formulas will help people find their way to safety without a handy computer.
Learning how to work formulas and apply them to real life is part of the modern world, and doing it without the aid of a computer is too time-consuming for many. The reason they are taught to do it in school is to help them understand the concept of what they are doing, and they can leave the math portion to their computers once they graduate.