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Cogito

Grade 7 Math · Chapter 7 · Lesson 3

Practice Worksheet

Area of a Circle

Why the radius is squared.

10 problems · about 19 minutes · 7.G.B.4

NameDate

Figure — use these to answer the problems

Change the radius. Watch how much faster the area grows than the circumference.
d = 10
  • Diameter10 cm
  • Circumference31.42 cm
  • Area78.54 cm²
  • Circumference ÷ diameter3.14
Radius5
Figure 1

Warm-Up Review

From earlier lessons. Loosen up before the new work.

3 problems

  1. From “Area of a Circle”

    Radius 4, π = 3.14. Area?

    Answer

  2. From “Measuring a Circle”

    Diameter 50, using π = 3.14. Circumference?

    Answer

  3. From “Solving Inequalities”

    4x > 20. Smallest whole number x?

    Answer

Warm Up

Straightforward practice. Get the method working first.

3 problems

  1. Diameter 16. What is r² ?

    Answer

  2. Radius 4. What is r² ?

    Answer

  3. Diameter 14. What is the radius?

    Answer

Build It Up

The same ideas with more to keep track of.

2 problems

  1. Radius 10. What is r² ?

    Answer

  2. Double the radius. How many times bigger is the area?

    Answer

Stretch Yourself

Mixed problems. Work out what kind of question it is before you start.

2 problems

  1. The Radius

    Radius 3. What is r² ?

    Answer

  2. The Diameter

    Diameter 12. What is r² ?

    Answer