Percentages are entered as decimals. For example 12% is entered as .12. You can format a cell to display the contents as percent, if you like.
Whats all the graph
Decimals and percentages are easier to compare than fractions - particularly if they are unlike fractions. That does not explain why percentages are required when we have decimal number and there is no good answer to that!
You should display an all around white light.
People use line graphs in businesses, and to compare data. Line graphs are mostly used when people are entrepreneurs. They figure out profit this way. Line graphs are also used when a product is made. They decide if they should continue to make this product, by how well the product sells. Line graphs show the change.
present information that is easy to see at a glance.
The sum of all percentages (in a circle graph or anywhere else) is 100%, which by definition is the totality of whatever it is that you are discussing.
they are display in the icons gone
Yes, if you use information from a graph, you should cite the reference.
It should consist of a short description of the variables which are plotted.