Mathematics
In 1-5= There are not so tough course, but as it comes to higher classes.
In 6-8= There are algebra, geometry, advanced no. Sys., etc.
So, as we are going to the higher class, we are going to next level we will get the tough and advanced mathematics, today, we are at this stage of the 21st century and it's time get more smart and quick to grassed up each and everything in a very quick and in responsive manner.