81. 2:1=X:8 X=2×8/1=16

6:2=X:8 X=8×6/2=48/2=24

2:22=X/8 X=8×2:22=16/22

5:4=X:8 X=5×8:4=10

82. X/4=8/3 X=4×8:3=32/3

7/X=9/5 X=7×5:9=35/9

6/1=X/3=6×3:17=18/17

85. 500/300=77/X X=300×77/500=46 100/500

87. 11/5=X/25 X=25×11:5=275/5=55

88. 160/X=8/56 X=160×56:8=1120

90. 13/2=1352/X X=1352×2:13=208