Idea 8of 22Builds onThe top view: looking straight down
Hidden cubes still count
How many cubes are in a building you can't see all of?
Today you'll discover
- why some cubes can't be seen
- how to know they are there
- how to count every cube
Think firstA big cube made of small cubes
How many small cubes make this big cube?
Decide first, then press Next. Look for a cube that must be there to hold up the ones above.
A big cube made of 8 small cubes, drawn from a corner: 7 can be seen. A dashed cube appears at the back of the bottom layer. Then the top view, with 2 written in each of its 4 squares, and the line 7 you can see plus 1 hidden equals 8 cubes. The last step asks about a block 3 long, 2 deep and 2 tall.
See the whole ideathe big idea and the key word, in one place
The big idea
Count the hidden cubes too: every cube on top needs cubes under it.
Why it happensCubes can't float. If you see a cube on top, there must be cubes under it, even out of sight.
Easy to get wrongA drawing from one corner never shows every cube. Don't count only the cubes you can see.
Key word
- hidden cube
- a cube in a building that you cannot see from where you look, because other cubes are in front of or on top of it
Ready to use it?
- Count the cubes in a building, hidden ones too.
- Find where a hidden cube must be.