原式=(20/1-20/2)-(59/2-59/3)+(103/3-103/4)-(149/4-149/5)+(191/5-191/6)-(223/6-223/7)+(239/7-239/8)-(243/8-243/9)+(199/9-199/10)-(131/10-131/11)+(23/11-23/12)
=20/1-79/2+162/3-252/4+340/5-414/6+462/7-482/8+442/9-330/10+154/11-23/12
=20-39-1/2+54-63+68-69+66-60-1/8+49+1/9-33+14-1-11/12
=6-1/2-1/8+1/9-11/12
=5-31/72
=4+41/72
