Calculate the circumference of a circular lake

Question

A lake has a diameter of $7$m and needs to be fenced for the protection for children.

1. What length of fencing is required?
2. Fencing comes in $1$m lengths, how many lengths are needed?
3. What is the total cost of the fencing if each length costs $25$ euro?

Can someone please help me answer these questions? I really don't understand them.

Answer 1

Hint:

The circumference of a circle with diameter $d$ is $C=\pi\cdot d$.

Answer 2

a) fencing material required should equal the circumference of the circular lake. $C = \pi d$, $d$ is diameter.

b) $\pi d \approx 3.14(7) = 21.98 \approx 22$. So you need $22$ lengths.

c) The total cost is $25\cdot 22 = 550$ euros.

Answer 3

Circumference of a circle is 2 pi r, area is pi r squared. They would need 7m*pi fencing. Using a calculator should give a decimal answer. Round up to the nearest meter to get your answer for b, and multiply your answer for b by 25 euro/meter.