L6 · Circumference and area of circles

1. 1.

   A circle has radius 9 cm. Find the circumference in terms of π.

   Answer. 18π cm

   C = 2πr = 2π(9) = 18π cm.

2. 2.

   A circle has radius 10 cm. Find the area in terms of π.

   Answer. 100π square cm

   A = πr² = π(10)² = 100π square cm.

3. 3.

   A circle has radius 2 cm. Find the circumference in terms of π.

   Answer. 4π cm

   C = 2πr = 2π(2) = 4π cm.

4. 4.

   A circle has radius 5 cm. Find the area in terms of π.

   Answer. 25π square cm

   A = πr² = π(5)² = 25π square cm.

5. 5.

   A circle has radius 8 cm. Find the circumference in terms of π. Write a complete answer — Malik will compare with a partner.

   Answer. 16π cm

   C = 2πr = 2π(8) = 16π cm.

6. 6.

   A circle has radius 6 cm. Find the area in terms of π. Write a complete answer — Sam will compare with a partner.

   Answer. 36π square cm

   A = πr² = π(6)² = 36π square cm.

7. 7.

   A circle has radius 2 cm. Find the circumference in terms of π. Write a complete answer — Priya will compare with a partner.

   Answer. 4π cm

   C = 2πr = 2π(2) = 4π cm.

8. 8.

   A circle has radius 9 cm. Find the area in terms of π. Write a complete answer — Luis will compare with a partner.

   Answer. 81π square cm

   A = πr² = π(9)² = 81π square cm.

9. 9.

   A circle has radius 8 cm. Find the circumference in terms of π. Write a complete answer — Sam will compare with a partner.

   Answer. 16π cm

   C = 2πr = 2π(8) = 16π cm.

10. 10.

    A circle has radius 6 cm. Find the area in terms of π. Write a complete answer — Priya will compare with a partner.

    Answer. 36π square cm

    A = πr² = π(6)² = 36π square cm.

11. 11.

    Think

    Ava tried this problem:
    A circle has radius 3 cm. Find the circumference in terms of π.
    Ava wrote 12π cm. That is not correct. What is the right answer?

    Answer. 6π cm

    Ava’s answer 12π cm is off. C = 2πr = 2π(3) = 6π cm.

12. 12.

    Think

    Priya tried this problem:
    A circle has radius 6 cm. Find the area in terms of π.
    Priya wrote 35π square cm. That is not correct. What is the right answer?

    Answer. 36π square cm

    Priya’s answer 35π square cm is off. A = πr² = π(6)² = 36π square cm.

Original extra practice. Keys are computed from the items, not guessed.