The width of the rectangle is 20cm, how will its area change if the length is increased by 4.

If the length of the rectangle is increased by 4 cm, then the area of this rectangle will change by the product of its width by the value by which the length was increased. So, in our case, the area will increase by:

4 * 20 = 80 (cm).

Let’s look at an example. Let the length of this rectangle be 30 cm.Let’s find its area:

S = 20 * 30 = 600 (cm²).

Let’s increase the length by 4 cm: 30 + 4 = 34 (cm).

Let’s find a new area:

S = 20 * 34 = 680 (cm²).

Let’s calculate the difference between the areas:

680 – 600 = 80 (cm²).

Answer: it will increase by 80 cm².