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7th grade · Math · Unit 5 of 18

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.

Alabama Course of Study content standard: 7.20 · 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 Alabama

In the Alabama Course of Study, this is unit 5 of 18 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: Alabama State Department of Education (ALSDE)

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 18 cm. Using 3.14 for π, what is its area?

    ⭕d = 18 cm
    • 56.52 cm²
    • 1017.36 cm²
    • 28.26 cm²
    • 254.34 cm²

  2. Question 2

    A circle has a diameter of 4 cm. What is its radius?

    ⭕d = 4 cm
    • 8 cm
    • 2 cm
    • 4 cm
    • 1 cm

  3. Question 3

    A round pizza has a diameter of 32 cm. What is the area of its top? Use 3.14 for π and round to one decimal place.

    🍕d = 32 cm

    answer boxcm²

  4. Question 4

    What is π (pi)?

    • The circumference divided by the diameter, about 3.14
    • The radius times 2
    • Half of the diameter
    • The distance around a circle

  5. Question 5

    A circle has a radius of 18 m. What is its circumference? Use 3.14 for π and round to one decimal place.

    ⭕r = 18 m

    answer boxm

  6. Question 6

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

    ⭕r = 7 cm

    answer boxcm²

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