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7th grade · Math · Unit 9 of 22

Circles

Circumference, area and π

What your child practices

Using radius, diameter and π (about 3.14) to find the distance around a circle and the area inside it, including real objects like wheels and pizzas.

Texas Essential Knowledge and Skills (TEKS) teks student expectation: 7.5(B); 7.8(C); 7.9(B) · π, and the circumference and area of circles

How we explain it

Children can open this short lesson before they practice.

  1. The radius goes from the center to the edge. The diameter goes all the way across: d = 2r.
  2. Circumference (the distance around) is C = π × d.
  3. Area is A = π × r × r. Use π ≈ 3.14.

Example: A circle has diameter 10 cm. What is its circumference? C = π × d. C ≈ 3.14 × 10 = 31.4. Answer: About 31.4 cm

Circles in Texas

In the Texas Essential Knowledge and Skills (TEKS), this is unit 9 of 22 in 7th grade Math, after Scale Drawings and before Volume.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: Texas Education Agency (TEA)

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    A circle has a radius of 4 cm. What is its area? Use 3.14 for π and round to one decimal place.

    ⭕r = 4 cm

    answer boxcm²

  2. Question 2

    A circle's circumference is 94.2 cm. What is its diameter? (Use 3.14 for π.)

    answer boxcm

  3. Question 3

    A circle has a radius of 7 m. What is its circumference? Use 3.14 for π and round to one decimal place.

    ⭕r = 7 m

    answer boxm

  4. Question 4

    If you double a circle's diameter, what happens to its circumference?

    • It becomes 4 times as long
    • It stays the same
    • It doubles
    • It grows by 3.14

  5. Question 5

    A circle has a diameter of 6 cm. What is its radius?

    ⭕d = 6 cm
    • 1.5 cm
    • 6 cm
    • 12 cm
    • 3 cm

  6. Question 6

    A circle has a diameter of 45 cm. What is its circumference? Use 3.14 for π and round to one decimal place.

    ⭕d = 45 cm

    answer boxcm

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