The second math problem in the third grade of primary school is what should be calculated in this way to illustrate the key understanding.

Area: We can use the complement method to calculate.

10× 10= 100 (square centimeter) This is the area of a big square.

(10-3)×( 10-3)=49 (square centimeter) This is the area of a square.

100-49=5 1 (square centimeter) This is the area of this graph.

There's another way.

10×3×2=60 (square centimeter) This is the area of two rectangles.

3×3=9 (square centimeter) This is the overlapping part.

60-9=5 1 (square centimeter) This is the area of this graph.

Perimeter: Perimeter is simpler.

10+ 10=20 (cm) This is the circumference of the outside.

(10-3)+(10-3) =14 (cm) This is the perimeter inside.

20+ 14=34 (cm) This is the perimeter of the graph.

I hope the above can help you!