7. A square piece of card has perimeter $20 \mathrm{~cm}$. Charlie cuts the card into two rectangles. The perimeter of one of the rectangles is $16 \mathrm{~cm}$. What is the perimeter of the other rectangle?
A $4 \mathrm{~cm}$
B $8 \mathrm{~cm}$
C $10 \mathrm{~cm}$
D $12 \mathrm{~cm}$
E $14 \mathrm{~cm}$
7. E The length of the edge of Charlie's original square is $(20 \div 4) \mathrm{cm}=5 \mathrm{~cm}$. Since he cuts his square into two rectangles, he cuts parallel to one side of the square to create two rectangles each with two sides $5 \mathrm{~cm}$ long as shown in the diagram.
Hence the total perimeter of his two rectangles is $2 \times 5 \mathrm{~cm}=10 \mathrm{~cm}$ longer than the perimeter of his square. Since the perimeter of one of the rectangles is $16 \mathrm{~cm}$, the perimeter of the other rectangle is $(20+10-16) \mathrm{cm}=14 \mathrm{~cm}$.