How many planks 3 m long and 3 dm wide do you need to lay the floor in a square room with a side of 6 m?

To solve this problem, recall the formula for the area of a rectangle. The area of a rectangle is equal to the product of its length and width. S = a * b, where a is the length and b is the width. Let’s convert decimeters to meters. 1 meter = 10 dm, 3 dm = 3/10 = 0.3 meters.
Let’s calculate what is the area of the board.
S = 0.3 * 3 = 0.9 sq.m.
Let’s calculate what the floor area is equal to. The area of a square is equal to the square of its side. S = a ^ 2.
S = 6 * 6 = 36 sq.m.
Let’s calculate how many boards are needed to cover the floor.
36 / 0.9 = 40 boards.
Answer: 40 boards.