Parts of a circle: radius, diameter, circumference and area

Answer Key - Grade 7 Math Worksheet - Building Confidence

Circle the best answer, or write your answer on the line.

1. 1.

   Ari's bike wheel has a radius of 35 cm. About how far does the bike roll in one full turn of the wheel? Use 3.14 for π.

   219.8 cm
2. 2.

   A round pond has a radius of 12 m. How far does Bo walk once around its edge? Use 3.14 for π.

   75.36 m
3. 3.

   A Ferris wheel has a radius of 45 ft. How far does a seat travel in one full turn, Esme? Use 3.14 for π.

   282.6 ft
4. 4.

   Jun's round rug has a radius of 28 in. How long is the fringe needed to go all the way around it? Use 3.14 for π.

   175.84 in
5. 5.

   Luz's round plate is 87.92 cm around. How many cm across (the diameter) is the plate? Use 3.14 for π.

   28 cm
6. 6.

   A tree trunk is 113.04 cm around. Milo wants its diameter, the distance straight across. Use 3.14 for π.

   36 cm
7. 7.

   Noah measures a round bowl and finds it is 69.08 cm around. How many cm across is the bowl? Use 3.14 for π.

   22 cm
8. 8.

   Pia measures three round things, distance around and across: a can (31.4 cm, 10 cm), a bucket (62.8 cm, 20 cm), a drum (94.2 cm, 30 cm). What does around ÷ across give?

   • About 3.14 each time, however big the circle is.
   • About 6.28 each time, because the distance around is two times 3.14 across.
   • About 2 each time, because the distance around is twice the distance across.
   • A bigger number for bigger circles, because a bigger circle has more distance around.
9. 9.

   Tala's round rug is 2 m across. Edge fringe is sold by the meter and top cleaner by the square meter. Which pair of amounts is right? Use 3.14 for π.

   • Fringe: 6.28 m (circumference). Cleaner: 3.14 square m (area).
   • Fringe: 12.56 m (circumference). Cleaner: 3.14 square m (area).
   • Fringe: 6.28 m (circumference). Cleaner: 12.56 square m (area).
   • Fringe: 3.14 m (area). Cleaner: 6.28 square m (circumference).
10. 10.

    Milo says a bike wheel that is 70 cm across rolls about 70 cm in one turn. Zee disagrees. Which response is best?

    • Milo is right, because one turn rolls the distance across, which is the 70 cm diameter.
    • One turn rolls the distance around, about 220 cm, a little over 3 times the 70 across.
    • One turn rolls about 35 cm, because the wheel rolls its radius each turn.
    • One turn rolls about 140 cm, because the distance around is twice the 70 cm across.