Page 115 - NUMINO Challenge_B1

13 Perimeter

Basic Concepts Sum of Perimeters

When a rectangle is cut horizontally or vertically into two, the sum of the
perimeters can be measured as shown below:

5 cm

3 cm 5 cm
Perimeter of rectangle: 16 cm 5 cm

Sum of perimeters when a rectangle is cut into two
(Perimeter of the original rectangle) (Length of the cut-out side of the rectangle) 2
16 5 2=26 cm

Example As shown below, a rectangular piece of paper that is 10 cm long
and 8 cm wide is cut along the dotted lines into eight rectangles.
Find the sum of the perimeters of the eight rectangles.

10 cm

8 cm

Class Notes

The perimeter of the original rectangle is cm. 10 cm
8 cm
When the rectangle is cut horizontally along the dotted line,

the total perimeter increases by 2 times its original length,

which is cm.

When the rectangle is cut vertically along the dotted lines, the

perimeter increases by 2 times its original width, which is

cm. Since the rectangle is cut three times, the perimeter

increases by 3 cm.

Therefore, the sum of the perimeters of the eight rectangles

is cm.

112 NUMINO Challenge B1