Solution: Here "□, δ, O" respectively represent some natural numbers.
Figures 1 and 2 are both squares and circles, but the results are 3 and 1 respectively, so there must be addition and subtraction. It is not difficult to imagine that the subtraction should be Figure 2.
□+O = 3；
O-□= 1。
It can be concluded that "O" means 2 and "□" means 1.
It can be understood from the first two figures that when the circle is inside, it is calculated by addition; When the circle is outside, the circle is regarded as the minuend;
Figures 3 and 4 show "□, △", and the results are 6 and 4 respectively. As you can imagine:
Because □ in Figure 3 means 1, △ should mean 5, that is,1+5 = 6;
In figure 4, it is: 5- 1=4.
There are "△" and "O" in the last picture, and "circle" is in it. As can be seen from the previous law, "addition calculation" should be used.
△+O=5+2=7。
So the "7" is filled in the brackets.
To tell the truth, such a topic is not a good topic, and the difficulty is almost as difficult as the composition of the college entrance examination. I believe that such a topic will not be used as an upgrade exam, but at most it can be placed in a "think about it" thinking question. This topic focuses on students' symbolic consciousness, and nothing else is done.