Subtract its 1/2: it can be understood as: × 1/2.

Subtract the remaining 1/3: it can be understood as: ×2/3.

Subtract the remaining 1/4: it can be understood as ×3/4.

……

Subtract the last remaining 1/20 10: it can be understood as ×2009/20 10.

(and so on), this problem can be listed as follows:

20 10× 1/2×2/3×3/4……×2009/20 10

= 2010×1/2010 (the result of cross reduction)

= 1