Gordon's tea shop has caffeinated tea and decaffeinated tea.

the tea shop served 14 caffeinated teas and 6 decaffeinated teas this morning.
what percentage of the teas served were caffeinated?

Total no. of teas served: 20

Therefore, we can write the two quantities as fractions of twenty:

14/20 and 6/20

A percentage is "per-cent", i.e. per 100, therefore a fraction of 100. To make this denominator a fraction of 100 we multiply it by 5 (20 x 5 = 100), and because what we do to the bottom of the fraction we must do to the top, we multiply each numerator by 5:

14/20; 14 x 5 = 70
6/20; 6 x 5 = 30

So,

70/100 , 30/100

70% of the teas sold were caffeinated.