10. As shown in the figure, a line segment $A B$ of length 9 is divided into nine equal parts, then the total length of all line segments in the figure is . $\qquad$
【Answer】165
【Analysis】All line segments include: 9 segments of 1 unit length, total length: $9 \times 1=9$
8 segments of 2 unit lengths, total length: $8 \times 2=16$
7 segments of 3 unit lengths, total length: $7 \times 3=21$
1 segment of 9 unit lengths, total length: $9 \times 1=9$

Therefore, the total length of all line segments is: $9 \times 1+8 \times 2+7 \times 3+6 \times 4+5 \times 5+4 \times 6+3 \times 7+2 \times$ $8+1 \times 9=165$
【Difficulty】
【Knowledge Point】Geometric Counting