Question 104282
The answer should be 275 square centimeters.  Here's why:


This is a surface area problem.



First, let me calculate the surface area of this box.  Let's assume that it is 10 cm tall, but that if you set it on a table, its base is 5 cm by 5 cm.  


Wouldn't you agree that the bottom and top will each have an area of 25 sq. cm.?
And each of the 4 sides will have an area of 10x5 or 50 sq. cm.?

Bases + Sides = total surface area
2(25)+4(50)=250 sq cm



Now we encounter trouble.  Apparently, some of the material was wasted while we made the box.  In fact, 10% of our final product.  Because of the way this problem was written, I am going to assume that we mean 10% of the 250 square centimeters was how much cardboard was wasted.  This would mean that 0.10(250) or 25 square centimeters of cardboard was wasted.  


Altogether, we would have 250+25 (or 275) square centimeters of cardboard needed.


This should be the correct answer, but IF your teacher MEANT to say that in the process, 10% of the ORIGINAL amount of cardboard was wasted, we would need to set up an equation like this:

0.90(x)=250

In other words, if 10% was wasted, then 90% is still there.  
90% of the original amount (x) is equal to 250.


If this is what your teacher meant, then the answer would be 250/0.90 or 
277.8 square centimeters.