The width of the rectangle is 30 mm. Find the lengths of the sides of this rectangle if its perimeter is 14 cm.

In the task, the width of the rectangle and its perimeter are known, while these values ​​are expressed in different units of measurement. We need to convert the width of the rectangle to the same unit as its perimeter. First, let’s write down how many millimeters are in one centimeter:

1 centimeter = 10 millimeters.

We translate the value of 30 millimeters into centimeters, for this we divide the number 30 by the number 10:

30/10 = 3 (cm) – the width of the rectangle.

Now let’s write down the formula for finding the perimeter of a rectangle:

P = (a + b) * 2,

Where a is the length, b is the width of the rectangle.

We do not know only the length, let’s make an equation and solve it:

(a + 3) * 2 = 14,

a + 3 = 14/2,

a + 3 = 7,

a = 7 – 3,

a = 4 (cm).

Answer: The rectangle is 4 cm long, 3 cm wide and 14 cm perimeter.