☰ Year plan · Mathematics

Term 1 review

Week 15 · Term 1 review · 3 lessons
2

Review: measures, area and perimeter

Discover Mathematics P4: Term 1, Units 1–8, Review
GoalReview units of measure, time, perimeter and area.
New words
perimeter · the distance around a shapearea · the number of square units that cover a shapeelapsed time · how much time passes from a start to an end
Explanation

Metric units change by powers of ten: 1 km = 1,000 m, 1 m = 100 cm, 1 cm = 10 mm, 1 kg = 1,000 g, 1 t = 1,000 kg and 1 L = 1,000 mL. To change to a smaller unit we multiply, to a bigger unit we divide. Time: 1 h = 60 min and 1 min = 60 s. For elapsed time, count up from the start to the next hour and then on to the end. A rectangle with length l and width w has perimeter P = 2 × (l + w) and area A = l × w. If we know the area and one side, divide to find the other side. If both sides double, the perimeter doubles but the area becomes 4 times as big.

ShapePerimeterArea
Rectangle l × w2 × (l + w)l × w
Square, side s4 × ss × s
Worked examples
FromToWork
3 km 250 m3,250 m3 × 1,000 + 250
4,800 g4 kg 800 g4,800 ÷ 1,000
2 L 75 mL2,075 mL2 × 1,000 + 75
Change units: 3 km 250 m = 3 × 1,000 + 250 = 3,250 m. 4,800 g = 4 kg 800 g. 2 L 75 mL = 2,075 mL.
A film starts at 9:40 a.m. and ends at 12:15 p.m. From 9:40 to 12:00 is 2 h 20 min, and 15 min more makes 2 h 35 min.
18 m7 m
A rectangle 18 m by 7 m: P = 2 × (18 + 7) = 50 m and A = 18 × 7 = 126 m². A rectangle with area 216 m² and length 18 m has width 216 ÷ 18 = 12 m, and perimeter 2 × (18 + 12) = 60 m.
Class activity

Measure the room. With a metre stick or tape, measure the length and width of a table or a room in cm. Find its perimeter and area, and change the perimeter to metres.

Practice
1
Change 5 m 40 cm to cm and 7,250 m to km and m.
2
A truck carries 3 t of bricks and unloads 1,250 kg. How many kg are left on the truck?
3
A film starts at 6:50 p.m. and lasts 1 h 45 min. When does it end?
4
A square has a perimeter of 36 m. Find its side and its area.
5
A rectangle is 6 cm by 4 cm. Both sides double. Find the old and new perimeters and areas.