Perimeter, area and units of measure
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Units of Measure
- Length is measured in millimetres (mm), centimetres (cm), metres (m), and kilometres (km).
- 1 cm = 10 mm, 1 m = 100 cm, 1 km = 1000 m.
- Mass is measured in grams (g) and kilograms (kg). 1 kg = 1000 g.
- Capacity (how much liquid a container holds) is measured in millilitres (ml) and litres (l). 1 l = 1000 ml.
- Time is measured in seconds (s), minutes (min), and hours (h). 1 min = 60 s, 1 h = 60 min.
- To convert from a larger unit to a smaller unit, multiply. For example, 3 m = 3 × 100 = 300 cm.
- To convert from a smaller unit to a larger unit, divide. For example, 5000 g = 5000 ÷ 1000 = 5 kg.
Perimeter of Polygons
- The perimeter is the total distance around a shape.
- For any polygon (a flat shape with straight sides), add the lengths of all its sides to find the perimeter.
- A rectangle has two lengths (l) and two widths (w). Its perimeter is P = 2 × l + 2 × w.
- You can also write the rectangle perimeter as P = 2 × (l + w).
- A square is a rectangle with all four sides equal. If one side is s, then P = 4 × s.
- For a shape made from rectangles, split it into rectangles, find the missing side lengths, then add all the outside edges.
Area
- Area is the amount of space inside a flat shape.
- Area is measured in square units, like square centimetres (cm2) or square metres (m2).
- You can find area by counting squares on a grid. Each full square counts as 1 unit.
- For a rectangle, area = length × width, written as A = l × w.
- For a square, area = side × side, written as A = s × s or A = s2.
- Remember: perimeter is the distance around, area is the space inside.
Telling Time
- An analogue clock has two hands: the short hand shows hours, the long hand shows minutes.
- On an analogue clock, each number represents 5 minutes. For example, if the minute hand points to 3, it is 15 minutes past the hour.
- A digital clock shows time as numbers, like 3:45.
- The 24-hour clock uses numbers from 00:00 to 23:59. For example, 3:45 PM is 15:45.
- To find a duration (how long something lasts), subtract the start time from the end time. For example, from 2:30 to 4:15 is 1 hour and 45 minutes.
- When subtracting times, you may need to borrow 60 minutes from the hour. For example, 4:15 - 2:30 = 3:75 - 2:30 = 1:45.
Solving Word Problems
- Read the problem carefully and underline the question.
- Identify what you need to find: perimeter, area, or time.
- Look for key words: 'around' or 'fence' often mean perimeter; 'inside' or 'cover' often mean area.
- Check that units are the same before calculating. Convert if needed.
- For perimeter problems, add all sides or use the rectangle formula.
- For area problems, multiply length by width.
- Always write the correct unit in your answer, like cm, cm2, or minutes.
Perimeter of a Circle (Circumference)
- The perimeter of a circle is called the circumference.
- The diameter (d) is the distance across a circle through its centre.
- The radius (r) is the distance from the centre to the edge. It is half the diameter: r = d ÷ 2.
- The circumference is about 3 times the diameter. The exact number is π (π), which is about 3.14.
- So the formula is C = π × d or C = 2 × π × r.
- For example, if a circle has a diameter of 10 cm, its circumference is about 3.14 × 10 = 31.4 cm.
Slide
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Soal latihan
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1.What is the perimeter of a shape?
Easy- AThe distance around the shape
- BThe space inside the shape
- CThe length of one side
- DThe width of the shape
2.Which unit would you use to measure the perimeter of a football field?
Easy- Ameters
- Bsquare meters
- Cliters
- Dgrams
3.The perimeter of a circle is called its circumference.
EasyTrue or false?
4.A square has side length 6 m. What is its perimeter?
Medium- A12 m
- B24 m
- C36 m
- D18 m
5.Which of the following are units of length? (select all that apply)
Easy- Akilometer
- Bkilogram
- Ccentimeter
- Dmilliliter
- Emeter
6.Match each shape to its perimeter formula.
Medium- Rectangle
- Square
- Triangle
- 2 × (length + width)
- 4 × side
- sum of all three sides
7.Put these lengths in order from shortest to longest: 5 cm, 1 m, 250 mm, 0.5 km.
Easy- 5 cm
- 250 mm
- 1 m
- 0.5 km
8.A rectangular garden is 15 m long and 10 m wide. How much fencing is needed to go around it once?
Medium- A25 m
- B50 m
- C150 m
- D100 m
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