The rule of the first group is that the latter number is twice as large as the former number, such as 1.2-0.4=0.8, 2.8- 1.5= 1.6, 6-2.8=3.2,, from which we can see that1.

The rule of the second group is that the latter number is 10 higher than the former number, for example, 30- 10=20, 60-30 = 30, 100-60 = 40, and it can be seen that 30-20= 10.