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A cube with 1 cm sides has a surface area of 6 cm2 and a volume of 1 cm3.
If the surface area is 49 cm2 then the edge lengths are 2.858 cm
If they are all the same size, the surface area is just the total surface area, which is 6 (faces) x edge x edge - that is the area of one face, (the length of one edge times itself as cubes have square faces) x the number of faces (6) x the number of cubes (3). Then subtract fom this the area not exposed, which is the top face of the bottom cube, top and bottom of the middle cube and bottom face of the top cube - so that's 4 faces. So the formula boils down to: 6 x 3 x edge x edge - 4 x edge x edge ... or ... 14 edge² If they are different sizes: 1. Work out the total area of each cube. 2. Between the bottom and middle cube, take the smaller and that face is hidden on both cubes, so subtract twice this face. 3. Do the same for the top and middle cubes.
To tackle this you first need to know the equations for both volume and surface area. The surface area of a cube is 6x2 where x is the side length. The volume of the cube is x3. Thus x is the cube root of the volume. We can substitute this in to the surface area equation and say that the surface area of a cube is 6volume2/3 This can also be rearranged to say that the volume of the cube is (the surface area/6)1.5
The total surface area is 150mm2 and the volume of the cube 125mm3