1/2 + 1/2*1/3
= 1/2 (1+1/3)
= 1/2*4/3
= 2/3九分之五乘十分之九减八分之三5/9*(9/10-3/8)= 5/9*9/10 - 5/9 *3/8= 1/2 - 5/24= 12/24 - 5/24= 7/245/9*9/10-3/8= 1/2 - 3/8= 4/8 - 3/8= 1/8