Question

На сколько процентов уменьшилась площа прямокутныка с сторонами 9см.и 20см.если их стороны уменьшить на 20%?

Answer 1

Ответ:

на 36%

Пошаговое объяснение:

S1 = a* b = 9 * 20 = 180 cм2.

9 - (9 * 0.2) = 7,2 см.

20 - (20 * 0.2) = 16 см.

S2 = a*b = 7,2 * 16 = 115,2 cм2.

180 -> 115.2 = 36%

Answer 2

Calculation of the Decrease in Area

To calculate the decrease in area of a rectangle with sides measuring 9 cm and 20 cm, when both sides are reduced by 20%, we can use the formula for the area of a rectangle, which is length multiplied by width.

Let's calculate the original area of the rectangle first:

Original area = length * width = 9 cm * 20 cm = 180 cm²

To find the new area after reducing both sides by 20%, we need to calculate the new length and width.

To reduce a value by a certain percentage, we can multiply the value by (100% - the percentage decrease). In this case, the percentage decrease is 20%, so we multiply by 80% (or 0.8).

New length = 9 cm * 0.8 = 7.2 cm New width = 20 cm * 0.8 = 16 cm

Now, let's calculate the new area:

New area = new length * new width = 7.2 cm * 16 cm = 115.2 cm²

To find the percentage decrease in area, we can use the formula:

Percentage decrease = (original area - new area) / original area * 100%

Percentage decrease = (180 cm² - 115.2 cm²) / 180 cm² * 100% ≈ 35.33%

Therefore, the area of the rectangle decreased by approximately 35.33% when both sides were reduced by 20%.