4, 1.2, 1.5 and 12___ ．

4, 1.2, 1.5 and 12___ ．

Because 1.2:0.4 = 3, 1.5:12 = 3, the composition ratio can be: 1.2:0.4 = 1.5:12 (the answer is not unique), so the answer is: 1.2:0.4 = 1.5:12

10 to 12 and 25 to 30, half to quarter and 9 to 6, 0.8 to 0.2 and four fifths to one fourth, which two ratios can form a proportion

10:12 = 5:6,
25:30 = 5:6,
Half to quarter = 1 / 2:1 / 4 = 2:1
9:6 = 3:2
2 = 4:1
Four fifths to one fourth = 4 / 5:1 / 4 = 16:5,
So: 10 to 12 = 25 to 30

Can half to one third, six to four make up the proportion
What about 0.6 to 0.2 and three quarters to one quarter

1/2:1/3=(1/2)*6:(1/3)*6=3:2
0.6:0.2=0.6*5:0.2*5=3:1
3/4:1/4=(3/4)*4:(1/4)*4=3:1

Is half to one-third

Three to two