2/3+2/15+2/35+2/63+2/99+1/11
=(1-1/3)+(1/3-1/5)+(1/5-1/7)+(1/7-1/9)+(1/9-1/11)+1/11
=1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11+1/11
=1

1/4X(4.85÷5/18-3.6+6.15×18/5）
=1/4×(4.85×18/5-3.6+6.15×18/5)
=1/4×[(4.85+6.15)×18/5-3.6]
=1/4×[39.6-3.6]
=1/4×36
=9
100X89+100X99-89X11-89X89/54X2+99X98+45X2
=(100-11-89)×89+100×99 /2×(54+45)+99×98
=100×99/2×99+99×98
=100×99/99×(2+98)
=100×99/99×100
=1
[14.8+(23/7-3/2)X28/25]÷21/5
=[14.8+23/7×28/25-3/2×28/25]÷21/5
=[14.8+92/25-42/25]÷21/5
=[14.8+2]÷21/5
=16.8×5/21
=4