Answer/Step-by-step explanation:
Square = 4 equal sides
1 side = 10 cm
So,
A+B+D+C = 10+10+10+10
so it equals 40
But we arfe looking for half of it or adding of the sides,
B+D
10 + 10 = 20
Answer = 20 cm
You could have also done it by :
The whole thing is 40, and a square has 4 sides. We are looking at 2 sides which is half so ,
40/2 = 20 cm
Answer: 20 cm
