Curriculum › Math ›Grade 6

Grade 6 Math · Level 4, Coordinate Geometry & 3D Geometry

Composite Polygon Area

How the lesson starts: Composite Polygon Area

1. Mila's Mini-Golf

   Fore! Welcome to Mila's Mini-Golf. Mila is laying fresh green turf on every hole. But her holes aren't plain rectangles. Some are L-shapes, and some have ponds! To find each area, we'll split shapes apart or cut pieces away.

2. Two ways for the L

   Hole 1 is an L-shape. Split it: the tall part is 3 by 5, that's 15. The top part is 4 by 2, that's 8. Add: 15 + 8 = 23. Or pretend it's a full 7 by 5 rectangle, 35, and take away the empty 4 by 3 corner, 12. 35 − 12 = 23. Same area either way!

3. A pond in the middle

   Hole 2 is 10 by 8 with a 3 by 4 pond in the middle. Turf doesn't go in the water, so subtract. The whole hole is 10 × 8 = 80. The pond is 3 × 4 = 12. 80 − 12 = 68 square units. Watch out: 80 is too big, because it covers the pond!