A cuboid water tank, the bottom is square, the water tank is 5 decimeters high, its four side area of a total of 200 square decimeters, the water tank can hold how many kilograms?

A cuboid water tank, the bottom is square, the water tank is 5 decimeters high, its four side area of a total of 200 square decimeters, the water tank can hold how many kilograms?

This is a problem of volume
A cuboid with a square bottom and equal sides
So the area of one side is 200 △ 4 = 50 square decimeters
The side area is equal to the side length × height of the bottom (because the bottom is square), so next, find the side length of the bottom, 50 △ 5 = 10 decimeters
This tank holds water 10 × 10 × 5 = 500 cubic decimeters

A rectangular tin water tank with a square bottom, if you unfold its side, you can just get a square with a side length of 6 decimeters to calculate the surface area

Rectangle bottom square perimeter = cuboid height = 6 decimeters
Side length of the square on the bottom of the cuboid = 6 △ 4 = 1.5 decimeters
Cuboid surface area = 1.5 × 1.5 × 2 + 6 × 6 = 40.5 square decimeters
A: the surface area of the cuboid is 40.5 square decimeters

Make a square iron sheet water tank without cover, the bottom area is 0.81dm2, at least how many square decimeters of iron sheet?

Iron sheet = 0.81 × 5 = 4.05 square decimeter