Originally I thought this was something complicated, like surface area or volume, in which the answer would have been hard to determine given the fact that trash bins are different widths at the top and bottom.
However, with the info you just gave me, I believe this is more of a simple circumference problem.
So, in math, you have a triangle of equations relating to pi. R*2=Diamater, Diameter*3.14=circumference, circumference/3.14=Diameter, etc.
So, here you are given the diameter of the top and radius of the bottom of the bin. The top is 25 cm (d), the bottom is 10 cm (r). ACROSS, First, you want to make both measurements the same.
So, leave 25cm (d) alone, but change the 10 cm (r) to diameter (d). So, radius *2= diameter, so 10*2=20, so the top is 25 cm (d) and the bottom is 20 cm (d).
Next you need to find the circumference (around the edge length, imagine the wrapper on a water bottle, that wrapper goes completely around the bottle and comes back to touch its end. That's circumference.)
So, circumference is diameter * pi (3.14, calculated originally by Archimedes, but pi is actually infinite digits)
So, 25*3.14 (use a calculator as expected) =78.5 And 20*3.14 =62.8
Add the two together to find out how much length of whatever she wants to put on the bin she needs.
78.5+62.8=141.3
You can round and say she needs 142 cm of decoration.
This is assuming that she wants to put 2 decorations on the bin, one on the top, one on the bottom, going around the bin, as that is what I understood from the question.
