1-5/6+7/12-9/20+11/30-13/42+15/56
=1-(1/2+1/3)+1/3+1/4-(1/4+1/5)+1/5+1/6-(1/6+1/7)+1/7+1/8
=1-1/2-1/3+1/3+1/4+.+1/7+1/8
=1-1/2+1/8
=1/2-1/8
=3/8
7.6乘31又2/5加43.9乘2又2/5
=(7+3/5)*(3+2/5)+(43+9/10)*(2+2/5)
=38/5*17/5+439/10*12/5
=1/25*19*17+1/25*6*439
=1/25(17*19+439*6)
=1/25*2957
=2957/25
=118+7/25
=118又7/25
（9又2/7加7又2/9）除以（5/7加5/9）
=(9+2/7+7+2/9)/(5/7+5/9)
=(65/7+65/9)/(5/7+5/9)
=[65(1/7+1/9)]/[5(1/7+1/9)]
=65/5
=13
（8-11/36）+(9-11/36*13）+（10-11/36*17）+（11-11/36*9）
=8+9+10+11-11/36-11/36*13-11/36*17-11/36*9
=38-11/36(1+13+17+9)
=38-11/36*40
=38-110/9
=38-(12+2/9)
=38-12-2/9
=26-2/9
=25+7/9