Square decimeter, Square meter
1.1. Square decimeter
 To measure area, we also use the following units: square decimeter.
 Square decimeter is the area of a square with side length 1dm.
 Square decimeter is abbreviated as dm^{2}.
We see a square of 1dm^{2} Includes 100 squares of 1cm^{2}
1dm^{2} = 100cm^{2}
1.2. Square meters
To measure area, we also use the following units: square meters.
Square meters is the area of a square with side length 1m.
Square meter is abbreviated as m^{2}.
We see a square of 1m^{2} including 100 squares of 1m^{2}.
1m^{2} = 100dm^{2}
1.3. Solve textbook exercises pages 63, 64
Lesson 1: Read : 32dm^{2} ; 911dm^{2 }; 1952dm^{2}; 492 000dm^{2}
Solution guide:
 To read the area measurement, we read the number first and then read the name of the symbol for that area.
32dm^{2} read as: Thirtytwo square decimeters ;
911dm^{2} read as: Nine hundred and one square decimeter ;
1952dm^{2} read: One thousand nine hundred and fiftytwo square decimeters;
492 000dm^{2} read: Four hundred and ninetytwo thousand square decimeters.
Lesson 2: Write according to the pattern
Read 
Write 
One hundred and two square decimeters 
102dm^{2} 
Eight hundred and twelve square decimeters 

One thousand nine hundred and sixtynine square decimeters 

Two thousand eight hundred and twelve square decimeters 

Solution guide:
 To write the measurement of an area, we write the number first and then write the symbol for that area.
Read 
Write 
One hundred and two square decimeters 
102dm^{2} 
Eight hundred and twelve square decimeters 
812dm^{2} 
One thousand nine hundred and sixtynine square decimeters 
1969dm^{2} 
Two thousand eight hundred and twelve square decimeters 
2812dm^{2} 
Lesson 3: Write the correct number in the dot
1dm^{2 }= … cm^{2 } 48 dm^{2 }= … cm^{2} 1997dm^{2} = … cm^{2}
100cm^{2} = … dm^{2 } 2000cm^{2} = … dm^{2} 9900cm^{2} = … dm^{2}
Solution guide:
 Based on conversion: 1dm^{2} = 100cm^{2}
1dm^{2} = 100cm^{2 } 48dm^{2 }= 4800cm^{2} 1997dm^{2} = 199700cm^{2}
100cm^{2} = 1dm^{2 } 2000cm^{2} = 20dm^{2 } 9900cm^{2} = 99dm^{2}
Lesson 4: Put >, <, = in the dot
210cm^{2 }… 2dm^{2}10cm 1954cm^{2 }… 19dm^{2}50cm^{2}
6dm^{2}3cm^{2}…603cm^{2 } 2001cm^{2}…20dm^{2}10cm^{2}
Solution guide:
 Convert both sides to the same unit of measure and compare the results.
+) We have: 1dm^{2 }= 100cm^{2} so 2dm^{2}= 200cm^{2}.
Hence: 2dm^{2}10cm^{2 }= 2dm^{2}+10cm^{2} = 200cm^{2}+10cm^{2} = 210cm^{2}.
So: 210cm^{2 }= 2dm^{2}10cm^{2}.
+) We have: 1dm^{2 }= 100cm^{2} so 19dm^{2 }= 1900cm^{2}.
Hence: 19dm^{2}50cm^{2 }= 19dm^{2}+50cm^{2} =1900m^{2}+50cm^{2 }= 1950cm^{2}.
Which: 1954cm^{2 }> 1950cm^{2}
So: 1954cm^{2 }> 19dm^{2}50cm^{2}.
+) We have: 1dm^{2} = 100cm^{2} so 6dm^{2 }= 600cm^{2}.
Hence: 6dm^{2}3cm^{2 }= 6dm^{2}+3cm^{2} = 600m^{2}+3cm^{2 }= 603cm^{2}.
So: 6dm^{2}3cm^{2 }= 603cm^{2}.
+) We have: 1dm^{2} = 100cm^{2} should be 20dm^{2 }= 2000cm^{2}.
Hence: 20dm^{2}10cm^{2 }= 20dm^{2}+10cm^{2} = 2000m^{2}+10cm^{2} = 2010cm^{2 }.
Which: 2001cm^{2 }< 2010cm^{2}
So: 2001cm^{2 }< 20dm^{2}10cm^{2}.
Lesson 5: Correct write D, false write WILL
a) A square and a rectangle have equal areas.
b) The area of the square and the area of the rectangle are not equal.
c) The area of the square is larger than the area of the rectangle.
d) The area of the rectangle is less than the area of the square.
Solution guide:
 Apply the formulas:
Area of rectangle = length x width;
Area of square = side x side
The area of the rectangle is:
20×5 = 100(cm^{2})
100cm^{2} = 1dm^{2}
The area of the square is:
1×1 = 1(dm^{2})
So the area of the square is equal to the area of the rectangle.
So we have the following result:
a) D b) S c) S d) S.
1.4. Textbook exercise solution page 65
Lesson 1: Write according to the pattern
Read 
Write 
Nine hundred and ninety square meters 
990m^{2} 
Two thousand zero hundred and five square meters 

1980m^{2} 

8600dm^{2} 

Twentyeight thousand nine hundred and eleven square centimeters 
Solution guide:
 To read (or write) area measurements we read (or write) the numbers first and then read (or write) the symbol of the unit of measurement.
Read 
Write 
Nine hundred and ninety square meters 
990m^{2} 
Two thousand zero hundred and five square meters 
2005m^{2} 
One thousand nine hundred and eighty square meters 
1980m^{2} 
Eight thousand six hundred square decimeters 
8600dm^{2} 
Twentyeight thousand nine hundred and eleven square centimeters 
28911cm^{2} 
Lesson 2: Write the correct number in the dot
1m^{2} = … dm^{2} 400dm^{2} = … m^{2}
100dm^{2} = … m^{2 } 2110m^{2} = … dm^{2}
1m^{2} = … cm^{2} 15m^{2} = … cm^{2}
10 000cm^{2} = … m^{2} 10dm^{2} = … cm^{2}
Solution guide:
 Apply 1m . conversion distance^{2} = 100dm^{2} ; 1dm^{2} = 100cm^{2}.
1m^{2} = 100dm^{2 } 400dm^{2 }= 4m^{2}
100dm^{2} = 1m^{2} 2110m^{2} = 211000dm^{2}
1m^{2} = 10000cm^{2} 15m^{2} = 150 000cm^{2}
10000cm^{2} = 1m^{2 } 10dm^{2}2cm^{2} = 1002cm^{2}
Lesson 3: To pave a room, 200 square bricks of side 30cm were used. How many square meters is that room, knowing the area of the grout circuit is negligible?
Solution guide:
 To calculate the area of 1 square brick, we multiply the side by the side.
 To calculate the area of the room, we multiply the area of 1 brick by the number of bricks used to pave the floor of that room.
 Convert the area measurement you just found to the unit of measurement is square meters.
Solution
The area of a floor tile is:
30×30 = 900(cm^{2})
Room size is:
900×200 = 180000(cm^{2})
180000cm^{2} = 18m^{2}
Answer: 18m^{2}.
Lesson 4: Calculate the area of a piece of cardboard with dimensions according to the figure below
Solution guide:
 Divide the given piece of cardboard into small rectangular pieces of cardboard and calculate the area of those shapes.
 The area of the cardboard is equal to the sum of the areas of the smaller pieces.
The given shape can be cut or divided into rectangles as follows:
Rectangle HOUSE_{first} whose width is equal to the width of the rectangle H_{2} and equal to 3cm.
Area of rectangle H_{first }is :
4×3 = 12(cm^{2})
Area of rectangle H_{2} is :
6×3 = 18(cm^{2})
Width of rectangle H_{3} is :
5–3 = 2(cm)
Area of rectangle H_{3} was:
15×2 = 30(cm^{2})
The area of the sheet is:
12+18+30 = 60(cm^{2})
Answer: 60cm^{2}.
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