Clearly, wether we're talking about tiles, plants, pages, e-mails, friend or files, the math won't change! :)
Percentages are just special fractions, since they have denominator 100. So, for example, 64% of 75 is given by
[tex]75\times \dfrac{64}{100} = 75\div 100 \times 64 = 0.75\times 64=48[/tex]
So, you divide the number by 100 and then you multiply by the percentage you want. As a last example, 20% of 70 is
[tex]70\times \dfrac{20}{100} = 70\div 100 \times 20 = 0.7\times 20=14[/tex]
And so on with all the others
