Question

The perimeter of a square is not more than 80 cm . What is the largest possible area of the square?

Answer 1

As perimeter gets bigger area gets bigger as well. Therefore a maximum perimeter specifies a maximum area,

You want to relate perimeter and area in order to figure out the answer.
you know that with side length you can determine either area or perimeter.
\(A=l^2\)
\(P=4l\)
therefore find the side length of the square by dividing by 4
40=4l
l=10
square this number to get your area
A=10*10
A=100 square centimeters

Answer 2

Thankyou @inkyvoyd :)

Answer 3

now, actually 80/4=20, so the answer is 400cm^2

Answer 4

I can't do arithmetic, but at least my reasoning works out.

Answer 5

I got it thankyou :)