Each friend got 1/5 of the pizza. If you cut a pizza into 5 slices, and you give the same amount to each of 5 friends, each friend will get 1 slice.
And 1/5 is 0.2 in decimal form
If there were multiple pizzas, just multiply 0.2 by the number of pizzas because each friend gets 0.2 of each pizza. (: