Final answer:
The correct answers are: C for the area of a circle with a 5mm radius, C for the circumference of a circle with a 20ft radius, and B for the area of a circle with a 20cm diameter.
Step-by-step explanation:
The area of a circle with a given radius can be calculated using the formula πr², where π (pi) is approximately 3.14159 and r is the radius of the circle. For a circle with a radius of 5mm, the area is π(5mm)², which equals 78.54mm² when calculated. This area should be rounded to the nearest tenth as 78.5mm², making option C the correct answer.
The circumference of a circle is given by the formula 2πr, where r is the radius. For a circle with a 20ft radius, the circumference is 2π(20ft) = 125.66ft, and rounding to the nearest tenth gives us 125.7ft, making option C the correct answer once again.
The area of a circle with a diameter of 20cm can be found by using the radius, which is half the diameter, so the radius in this case is 10cm. Using the formula for the area of a circle, we get π(10cm)² = 314.16cm², and by rounding to the nearest tenth, we find the area to be 314.2cm², corresponding to option B.