The circumference of a circle is 8 TT cm. What is the RADIUS of the circle? A)
2 cm
B)
4 cm
C)
6 cm
D)
8 cm

Q6. The answer is D)8 cm.

The circumference (C) of a circle with radius r is: C = 2r π
The diameter (d) of a circle is double its radius r: d = 2r

Therefore, the circumference of a circle can be written as: C = d π

If the circumference of a circle is 8π cm: C = 8π cm, then
C = d π = 8π cm
d π = 8π cm

Divide π from both sides:
d π / π = 8π cm / π
d = 8 cm
Thus, the diameter of the circle is 8 cm.

Q7. The answer is C) 2π

The circumference (C) of a circle with radius r is: C = 2 r π
Therefore, if r is known, to calculate C, 2π must be added to r.

For example, r = 4
C = 4 * 2π = 8π

Q8. The answer is D)Multiply the diameter by 3.14 to find the circumference

The circumference of a circle is:
C = 2r π
C - the circumference
r - the radius
π = 3.14 (mathematical constant)

However, the diameter of a circle is twice of its radius:
d = 2r
Hence, the circumference can be expressed as: C = d * π

Since Allison knows the diameter of the circle, she must multiply it by π to get the circumference, i.e. she must multiply the diameter by 3.14 (since π = 3.14)

Q9. The answer is B)First measure the diameter then multiply that by π to find the circumference.

The first Devin's statement "First measure the radius (r), then multiply that by 2, then multiply that answer by π, and that will give you the circumference (C)." can be expressed as:
r * 2 * π = C

But, it should be taken into consideration that the sum of two radius (r) is the diameter (d) of the circle: d = 2r

So, C = 2 r π = d π

So, another statement should be: "First measure the diameter then multiply that by π to find the circumference.";
d * π = C

Q10. The answer is D)1056.25 π

The circumference (C) of the circle with radius r is:
C = 2r π

C = 65 π
2r π = 65 π

Divide both sides by π:
2r π / π = 65 π / π
2r = 65
r = 65/2
r = 32.5

The area (A) of the circle with radius r is:
A = r²π
r = 32.5

A = (32.5)²π
A = 1056.25 π