Question

1+21/6+31/12+41/20+51/30+61/42+71/56+81/72+91/90

Answer 1

1+2又1/6+3又1/12+4又1/20+5又1/30+6又1/42+7又1/56+8又1/72+9又1/90
=（1+2+3+4+5+6+7+8+9）+（1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90）
=（1+9）×9÷2+（1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10）
=45+（1/2-1/10）
=45+0.4
=45.4

Answer 2

1+21/6+31/12+41/20+51/30+61/42+71/56+81/72+91/90
= 1+4-1/2+2+3/4+2+1/20+2-3/10+1+19/42++1+15/56+1+1/8+1+1/90
=15-1/2+3/4+1/20-3/10+19/42+15/56+1/8+1/90
=15-1/2+3/4+1/8+1/20-3/10+19/42+1/7+1/8+1/9-1/10
=15+1/2-7/20+19/42+1/7
=15+3/20+25/42
=15+313/420