Let's solve plane figures problems!
Stage 1,2,3,4,5,6 have easy problems.
Stage 7,8,9 have hard problems.
Stage 10 have very hard problems.
It is ok even if you cannot solve it.
You can ask your firends the ploblem by pushing a button of Twitter or Facebook.
The area of the 1x1 square is 1.
You can draw lines on the picture.