The perimeter of the rectangle is 40 cm. Find its width if the length is 11.

Let’s find the width of the rectangle, provided that we know its perimeter, which is 40 cm, and the length = 11 cm.

The sum of all sides of such a figure is calculated by the formula:

P = 2a + 2b.

Substitute the values known by the setting condition and write down the equation:

2 * 11 + 2b = 40.

We leave the variable with the coefficient on the left side of the equation, and move the number to the right, while the sign in front of it is changed to the opposite:

2b = 40 – 22 = 18.

To find the second factor, divide the product by the first:

b = 18: 2 = 9 cm – the width of the rectangle.