What this guide covers
Selected Sec 1 G5 plane-area and square-unit skills. Cylinders and composite solids are part of the wider level scope but are not taught in this focused guide.
Area counts square units
Sketch or label component regions. For a trapezium, use the perpendicular height. When changing metres to centimetres, square the length conversion for area.
Subtract a clearly defined region
A 12 cm by 8 cm rectangular card has a 3 cm by 3 cm square cut from its interior. Find the area left.
- Full rectangle area =12×8=96 cm².
- Removed square area =3×3=9 cm².
- Area left =96−9=87 cm².
Check: The answer is below 96 cm², as removing a square must reduce area.
Try it yourself
Work on paper, then compare the steps. These checks do not establish mastery.
A trapezium has parallel sides 7 cm and 13 cm and perpendicular height 6 cm. Find its area.
Area =½(7+13)×6=60 cm². The height must be perpendicular to the parallel sides.
Convert 0.08 m² to cm² and explain why multiplying by 100 is wrong.
Since 1 m²=100² cm²=10,000 cm², 0.08 m²=800 cm². Multiplying by 100 converts a length, not an area.
Where this connects
- Sec 1 mensuration scope →
See the other area, volume and unit skills in this level.
- Next: cones, spheres and pyramids →
Sec 2 extends measurement to further standard solids.
Sources and scope
Original Mentora examples and checks aligned to selected Sec 1 G5 skills in the MOE G2/G3 Mathematics syllabus. The rectangular cut-out is completely specified in words; no paper diagram was used.