Look at A 1 = 12, A2 = 8, B 1 = 12, B2 = 10, C 1 = 24, C2 = 10.

Then the interval of the center is [max(a2, b2, c2), min (A 1, B 1, C 1)] =

[max(8， 10， 10)，min( 12， 12，24)]=( 10， 12)

It's that simple.

In fact, it is easier for primary school students to do it.

The process is as follows

Draw three lines on the coordinates of A, B and C, and the overlapping part is the desired answer. You can draw it yourself.