According to the magician's cutting method, there is not a straight line in the middle after splicing, but two "broken lines".

It can be calculated that the middle "overlap" is exactly 1 decimeter.

As shown in the figure: AC = 5+2 = 29, BC = 8+3 = 73, AB = 13+5 = 194.

The formula of "tridiagonal quadrature" from Qin dynasty;

Square of ABC area of triangle

=( 1/4)[ac^ab^-((ac^+ab^-bc^)/2)^]

=( 1/4)[29* 194-((29+ 194-73)/2)^]

=( 1/4)[5626-75^]

= 1/4

The area of triangle ABC is S= 1/2.

Overlapping area =2S= 1

Here are the pictures.