This is a question of geometric series. If 1/3m is cut off, 1-( 1/3) metres remain; The 1/3 section in this problem is not the actual length, but the proportion, which is less than the unit 1-( 1/3) 1/3. Find the fraction of a number by multiplication, and use the fraction of this number x to leave 1x (. The second time, with the same proportion, multiply by (1- 1/3)… cut n times and (1- 1/3) n, cut four times and (1-kloc-0//3) 4.