6.5: x = 0.5:4 X: 0.42 = 7:21 1 / 8:1 / 6 = 1 / 10: x 6 / 2.5 = x / 3 3 / 2:1 / 3 = x: 8 x: 9 / 2 = 1 / 3:2 (solution ratio) 6.5: x = 0.5:4 X: 0.42 = 7:21 1 / 8:1 / 6 = 1 / 10: x 6 / 2.5 = x / 3 3 / 2:1 / 3 = x: 8 x: 9 / 2 = 1 / 3:2 (solution ratio)

6.5: x = 0.5:4 X: 0.42 = 7:21 1 / 8:1 / 6 = 1 / 10: x 6 / 2.5 = x / 3 3 / 2:1 / 3 = x: 8 x: 9 / 2 = 1 / 3:2 (solution ratio) 6.5: x = 0.5:4 X: 0.42 = 7:21 1 / 8:1 / 6 = 1 / 10: x 6 / 2.5 = x / 3 3 / 2:1 / 3 = x: 8 x: 9 / 2 = 1 / 3:2 (solution ratio)

6.5:x=0.5:4
x=4*6.5/0.5=52
x:0.42=7:21
x=7*0.42/21=0.14
1/8:1/6=1/10:x
x=(1/6)*(1/10)/(1/8)=2/15
6/2.5=x/3
x=6*3/2.5=7.2
3/2:1/3=x:8
x=(3/2)*8/(1/3)=36
x:9/2=1/3:2
x=(1/3)*(9/2)/2=3/4

3.5:0.4 = x: 8 x: 3 = 2.8:4 42: x = 3:6 5.4:2.7 = 0.4: x 0.4: x = (1 + one seventh): 5 solve these ratios

3.5：0.4=x：8
0.4x=3.5×8
0.4x=28
x=28÷0.4
x=70
x：3=2.8:4
4x=3×2.8
x=3×2.8÷4
x=2.1
42：x=3:6
3x=42×6
x=42×6÷3
x=84
5.4:2.7=0.4：x
5.4x=2.7×0.4
x=2.7×0.4÷5.4
x=0.2
0.4: x = (1 + one seventh): 5
8x/7=0.4×5
x=7/8×4
x=7/2

3 / 4: x = 3:12 (solution ratio)

The key to the solution is to apply "the product of internal terms equals the product of external terms"
x*3=3/4*12
x*3=9
x=3