What this lesson shows
A trapezoid with parallel sides 6 and 12, height 4, and slanted sides 5. Cut it into a 6 by 4 rectangle and two triangles with base 3 and height 4. 24 plus 6 plus 6 is 36 square units, the same as half of 6 plus 12, times 4. Its perimeter, 6 + 12 + 5 + 5, is 28 units.
The worked example
The lesson works this one step by step: a trapezoid, sides 6 and 12, height 4, slanted 5: area. Then your kid tries one like it on paper.
The steps
- Cut into a rectangle and 2 triangles
- Triangle: half of base × height
- Trapezoid: half of the parallel sides added, × height
- Perimeter: add all 4 sides
- Area in square units, perimeter in units
Helping at home
For the area, cut straight down from each end of the top: a rectangle and two triangles. Add their areas, or take half of the parallel sides added, times the height. For the perimeter, add all four sides. Area is in square units; perimeter is a length.
If your kid gets stuck
Area or perimeter? Which sides do you need?
Watch it with Lux
With Lux, this lesson is a narrated video and a printed page your kid works on. Then Lux helps with the same math on their own worksheet, one question at a time.
More in this unit
- Triangles two ways
- Every name that fits
- Not only the last name
- Solid figures
- Turning does not change it
- Volume by packing cubes
- No gaps, no overlaps
- Volume by formula
- The base is an area
- Find the missing edge
- Two boxes put together
- Nets of solids
- Area of parallelograms and triangles
- The angles of a triangle
- Estimating around a curve
- Radius and diameter
- Perimeter, area, or volume?
- Surface area with a net