Question 12
In a children’s carpentry contest, Trung builds a staircase one cube thick from wooden cubes as shown. A 2-step staircase uses 3 cubes; a 3-step staircase uses 6 cubes. Painting one small cube face takes 10 ml of paint. How many 500 ml cans are needed to paint every outside face of a 10-step staircase, including its underside?
