Rodrigo was to a stationary store and bought three notebooks. These notebooks were in sale. If you buy one notebook, the second and the third notebooks that you buy, will have 20% and 40% off, respectively.
In the next day, Gustavo was to the same stationary store and bought three notebooks too, but these notebooks weren't in sale anymore.
In percentage, how much Rodrigo paid unless than Gustavo?
Note: Rodrigo and Gustavo brought the same kind of notebooks.
Problem Source: OBMEP 2014