Grade 8Mathpractice16 questions

Circumference and area of circles

Grade 8: circumference = pi x diameter, area = pi x radius squared, pi is about 3.14, radius from diameter, area of a semicircle.

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Free to play. Teams answer on one screen; your phone is the remote. No student devices.

Questions

  1. Which formula gives the circumference of a circle with diameter d?

    • 2 × d
    • π × d
    • π × d ÷ 2
    • π × d²
    Show answerπ × d

  2. A circle has diameter 10 cm. Using π = 3.14, what is its circumference?

    • 15.7 cm
    • 31.4 cm
    • 314 cm
    • 62.8 cm
    Show answer31.4 cm

  3. A round pond has diameter 5 m. Using π = 3.14, what is its circumference?

    • 15.7 m
    • 31.4 m
    • 7.85 m
    • 78.5 m
    Show answer15.7 m

  4. Which formula gives the area of a circle with radius r?

    • 2 × π × r
    • π × d
    • π × r × 2
    • π × r²
    Show answerπ × r²

  5. A circle has radius 3 cm. Using π = 3.14, what is its area?

    • 18.84 cm²
    • 28.26 cm²
    • 84.78 cm²
    • 9.42 cm²
    Show answer28.26 cm²

  6. A circle has radius 10 cm. Using π = 3.14, what is its area?

    • 31.4 cm²
    • 314 cm²
    • 3140 cm²
    • 62.8 cm²
    Show answer314 cm²

  7. A circular plate has diameter 20 cm. What is its radius?

    • 10 cm
    • 20 cm
    • 40 cm
    • 5 cm
    Show answer10 cm

  8. A circle has diameter 8 cm. Using π = 3.14, what is its area?

    • 100.48 cm²
    • 200.96 cm²
    • 25.12 cm²
    • 50.24 cm²
    Show answer50.24 cm²

  9. A circle has area 314 cm² (π = 3.14). What is its radius?

    • 10 cm
    • 100 cm
    • 31.4 cm
    • 5 cm
    Show answer10 cm

  10. A semicircle is half of a circle with radius 10 cm. Using π = 3.14, what is its area?

    • 157 cm²
    • 314 cm²
    • 62.8 cm²
    • 78.5 cm²
    Show answer157 cm²

  11. The value 3.14 is only an approximation of pi. (True or false?)

    Show answerTrue

  12. If you double the radius of a circle, its area also doubles. (True or false?)

    Show answerFalse

  13. The area of a semicircle is half the area of the full circle with the same radius. (True or false?)

    Show answerTrue

  14. A circle has circumference 31.4 cm. Using π = 3.14, what is its diameter in cm? (Answer out loud)

    Show answer10 cm

  15. What is the radius of a circle with diameter 14 cm? (Answer out loud)

    Show answer7 cm

  16. A semicircle has radius 2 cm. Using π = 3.14, what is its area in cm²? (Answer out loud)

    Show answer6.28 cm²

Play it as a game

Line of FourAnswer right to drop a disc in any column. Four of your discs in a line score +5.Team BingoEvery team has a bingo card of answers. Each answer is called after its question. Three in a row: BINGO +5.Memory MatchAnswer right to flip two cards. Find a word and its picture to win the pair (+2), then the class says the word.Mystery PictureEvery right answer removes a piece. Name the picture first for a big bonus.

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