A - B = B

B * C = A

D : B = E

C * C = E

C + E = A

For which numbers stand A, B, C, D and E?

Can you connect all nine dots with only four straight line segments without losing contact with the paper while drawing?

The pieces with the same color in left figure have the same size as in the ones in the right figure. In the right image the pieces are only ordered differently. How to explain the hole in the right image?