The vertex of a cube with a side length of three decimeters has been dug out, and a cube with a side length of one decimeter has been dug out, But do you have some simple formulas? As a sixth grade student, I really can't understand them.

The vertex of a cube with a side length of three decimeters has been dug out, and a cube with a side length of one decimeter has been dug out, But do you have some simple formulas? As a sixth grade student, I really can't understand them.

Because a one decimeter cube is dug out from the top of the cube, the surface area of the remaining part is equal to that of the cube, so the remaining surface area is 3 * 3 * 6 = 54 square decimeters

A cube with an edge length of 5cm, and a cube with a side length of 2cm in the middle, the surface area and volume of the remaining figure are calculated
Who is right

Upstairs is not thoughtful, this is a concave solid, surface area has repeated calculation, surface area = 5 * 5 * 6 + 2 * 2 * 6-2 * 2-2 * 2 = 166 (square centimeter) volume = 5 * 5 * 5-2 * 2 * 2 = 125-8 = 117 (cubic centimeter) don't consider, my right, who can directly dig a cube from the heart, can only start from the surface, so

When the length of a square increases by 10%, its area increases ()
A. 10%B. 21%C. 30%D. 2.5%

Let the original length of the square be 1; the original area be 1 × 1 = 1; 1 × (1 + 10%), = 1 × 110%, = 1.1; 1.1 × 1.1 = 1.21; (1.21-1) △ 1, = 0.21 △ 1, = 21%; a: the area is increased by 21%