17/20×2/3+17/20×1/3-1/2=17/20×(1/3+1/3)-1/2=17/20-1/2=7/20(3/4-4/9)×36=3/4×36-4/9×36=27-16=11
17/20×2/3+17/20×1/3-1/2=17/20×﹙2/3+1/3﹚-1/2=17/20×1-1/2=17/20-1/2=17/20-10/20=7/20 ﹙3/4-4/9﹚×36=3/4×36-4/9×36=27-16=11