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7th grade · Math · Unit 5 of 17

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.

Maine Learning Results learning standard: 7.G.B.4 · 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 Maine

In the Maine Learning Results, this is unit 5 of 17 in 7th grade Math, after Two-Step Equations 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: Maine Department of Education

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 diameter of 12 cm. Using 3.14 for π, what is its area?

    ⭕d = 12 cm
    • 452.16 cm²
    • 18.84 cm²
    • 37.68 cm²
    • 113.04 cm²

  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 diameter of 23 cm. What is its circumference? Use 3.14 for π and round to one decimal place.

    ⭕d = 23 cm

    answer boxcm

  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 grows by 3.14
    • It doubles

  5. Question 5

    A round pizza has a diameter of 40 cm. What is the area of its top? Use 3.14 for π and round to one decimal place.

    🍕d = 40 cm

    answer boxcm²

  6. Question 6

    A circle has a radius of 11 cm. What is its area? Use 3.14 for π and round to one decimal place.

    ⭕r = 11 cm

    answer boxcm²

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