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Area: Circles

Area: Circles. PRE-ALGEBRA LESSON 10-3. (For help, go to Lesson 4-7.). Simplify each expression. 1. 3.14 • 4 2 2. 3.14 • 5 2 3. 3.14 • 9 2 4. 3.14 • 0.5 2. Check Skills You’ll Need. 10-3. Area: Circles. PRE-ALGEBRA LESSON 10-3. Solutions 1. 3.14 • 4 2 2. 3.14 • 5 2

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Area: Circles

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  1. Area: Circles PRE-ALGEBRA LESSON 10-3 (For help, go to Lesson 4-7.) Simplify each expression. 1. 3.14 • 422. 3.14 • 52 3. 3.14 • 924. 3.14 • 0.52 Check Skills You’ll Need 10-3

  2. Area: Circles PRE-ALGEBRA LESSON 10-3 Solutions 1. 3.14 • 422. 3.14 • 52 = 3.14 • 4 • 4 = 3.14 • 5 • 5 = 50.24 = 78.5 3. 3.14 • 924. 3.14 • 0.52 = 3.14 • 9 • 9 = 3.14 • 0.5 • 0.5 = 254.34 = 0.785 10-3

  3. A = r 2 1 2 = (10)2r = d; r = 10 = 100 Simplify. The area is 100 in.2. Area: Circles PRE-ALGEBRA LESSON 10-3 Find the exact area of a circle with diameter 20 in. Quick Check 10-3

  4. A = r 2 = (50)2r = d; r = 50 = 2,500 exact area 1 2 (2,500)(3.14) Use 3.14 for . Area: Circles PRE-ALGEBRA LESSON 10-3 A TV station’s weather radar can detect precipitation in a circular region having a diameter of 100 mi. Find the area of the region. = 7,850 approximate area The area of the region is about 7,850 mi2. Quick Check 10-3

  5. Area of region that is one fourth of a circle: area of circle = r 2 area of quarter circle = r 2 A (3.14)(15)2 Replace with 3.14 and r with 15. = 176.625 ft2 1 4 1 4 Area: Circles PRE-ALGEBRA LESSON 10-3 A pound of grass seed covers approximately 675 ft2. Find the area of the lawn below. Then find the number of bags of grass seed you need to buy to cover the lawn. Grass seed comes in 3-lb bags. 10-3

  6. 1,302 ÷ 675 1.93 Divide to find the number of pounds of seed. Area: Circles PRE-ALGEBRA LESSON 10-3 (continued) Area of region that is a rectangle: area of rectangle = bh A = 45 • 25 Replace b with 45 and h with 25. = 1,125 ft2 The area of the lawn is about 177 ft2 + 1,125 ft2 = 1,302 ft2. You need to buy one 3-lb bag of grass seed. Quick Check 10-3

  7. 256 in.2 Area: Circles PRE-ALGEBRA LESSON 10-3 Find the area. 1. Find the exact area of a circle with diameter 32 in. 2. A 5-ft-diameter round table is in a 12 ft-by-15 ft room. a. What is the area covered by the table? Round to the nearest unit. b. What is the area of the rest of the room? Round to the nearest unit. 20 ft2 160 ft2 10-3

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