Counting a 4 × 3 × 2 prism layer by layer
Let's count the unit cubes inside this rectangular prism — but the smart way, layer by layer.
Here's our shape, made of small unit cubes. Notice it's built from two equal layers stacked on top of each other.
Look at the bottom layer first. It's a flat slab of cubes, four across and three back.
Each row in this layer has four cubes.
And there are three rows in the layer.
So one layer holds four times three — that's twelve cubes.
The top layer looks exactly the same. Same shape, same twelve cubes.
Two equal layers means twelve times two.
Twelve times two is twenty-four. Our prism has twenty-four unit cubes in all!
Now you try. Count the unit cubes in this solid. How many unit cubes?