The length of the rectangle is 8 cm. This is two-fifths of its perimeter. What is the width of the rectangle.

1) We calculate the perimeter of the rectangle, provided that its length, equal to 8 cm, is from P 2/5 part:

8 * 5: 2 = 40: 2 = 20 cm.

2) Since the opposite sides of the rectangle are equal, the sum of its sides is calculated by the formula:

P = 2a + 2b. Let us express the width of this shape from this formula:

2b = P – 2a = 20 – 2 * 8 = 20 – 16 = 4. To find the second factor, divide the product by the first:

b = 4: 2 = 2 cm – the width of the rectangle.