|
First, paint the top and bottom
of the outside...
The top is a 10x10 square, so 100 little cubes get painted.
The bottom is a 10x10 square, so 100 little cubes get painted.
That's 200 so far...
Now, paint the front and back
of the outside...
The front is a 10x10 square...
that's 100 little cubes... But, we've already counted the
top stripe of cubes and the bottom strips since these got hit
when we did the top and bottom. So, for the new little
cubes we're hitting, we have an 8x10 grid... that's 80
more little cubes getting painted.
Same for the back... another
80.
So far: 100 + 100 + 80 +
80
Now, we do the left and right
side of the big cube... Thinking about it the same way we
did above, we'll be hitting an 8x8 set of new cubes with
paint... That's 64 for the right side and 64 for the left
side.
Total:
100 + 100 + 80 + 80
+ 64 + 64
= 488 |
