It is inevitable that the surface area will always decrease after splicing into a cuboid, because there are always two faces hidden, that is to say, the areas of the two faces will decrease;

The original surface area of a cuboid is (5*3+5*4+3*4)*2.

So the surface area of two cuboids is (5*3+5*4+3*4)*2*2.

When the reduced surface is the smallest, the surface area is the largest; (The area of 3*4 faces is the smallest, reducing two faces)

When the converted surface area is the largest, the surface area is the smallest; (The area of 5*4 faces is the largest, and two faces are reduced)

So the maximum value is: (5 * 3+5 * 4+3 * 4) * 2 * 2-3 * 4 * 2 =188-24 =164 (square centimeter).

The minimum is: (5 * 3+5 * 4+3 * 4) * 2 * 2-5 * 4 * 2 =188-40 =148 (square centimeter).

Seek adoption