Math can be done in many different ways and people are always finding new ways to solve problems. The short cuts shown in those videos are useful and different than i've seen before which was really interesting. The first video showed the cross multiplying way through mental math. The next two videos are about using lines that intersect to fins the solution. Although the tricks may be useful they are obsolete considering this is a college class where everyone has calculators or their phones to type out the problem for them. Yes, the japanese system is cool but is more time consuming than a calculator.