Question

Twenty circular pieces of pastry, each of diameter 4 cm, are cut from a rectangular layer of pastry 20 cm long and 16 cm wide. What is the area, correct to two decimal places, of pastry remaining after the 20 pieces are removed?

Answer 1

The area of the original pastry left is 68.67 cm^2

Explanation:

firstly, we need the area of the original total pastry

Mathematically, we have this as the product of the side lengths

this would be 20 cm * 16 cm = 320 cm^2

Now, for the circular pastry, we have a diameter of 4 cm

The radius is half of this which is 4 cm/2 = 2 cm

The area of a circular pastry will be = pi * r^2

The area of 20 will be 20 times the above

so we have 20 * pi * 2^2 = 251.33 cm^2

So, to get the area left, we subtract this from the original area

that would be;

320 cm^2 - 251.33 cm^2 = 68.67 cm^2