Same Area / Perimeter Challenge (CCSS 3.MD.D.8)
Same Area, Different Perimeter: Rectangles with the exact same space inside (Area = $w \times h$) can have totally different boundary lengths (Perimeter = $2w + 2h$). Long & skinny shapes have larger perimeters!
Same Perimeter, Different Area: Rectangles made with the same fence length can enclose different amounts of space. Square-like shapes enclose the maximum possible area!