Curriculum › Math ›Grade 6

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

Surface Area from Nets

How the lesson starts: Surface Area from Nets

1. Chef Bo's box cakes

   Welcome to Chef Bo's Box Cake Bakery! Bo bakes cakes shaped like boxes and covers every single face with frosting, even the bottom, because Bo is a little silly. How much frosting? Add up the area of every face. That total is called surface area!

2. A cube cake

   First, a cube cake with sides of 5 cm. Unfold it into a net: 6 matching squares. One face is 5 × 5 = 25 cm². There are 6 faces, all the same. So 6 × 25 = 150 cm² of frosting! The net shows every face, so none gets missed.

3. A long box cake

   Now a cake 6 cm by 4 cm by 3 cm. Its net has three face sizes: 6 × 4 = 24, 6 × 3 = 18 and 4 × 3 = 12. Each size shows up twice: top and bottom, front and back, left and right. So 24 + 18 + 12 = 54, and 2 × 54 = 108 cm². Watch out: 54 frosts only half the cake!