Area: Circles PRE-ALGEBRA LESSON 10 -3 (For help, go to Lesson 4 -7. ) Simplify each expression. 1. 3. 14 • 42 2. 3. 14 • 52 3. 3. 14 • 92 4. 3. 14 • 0. 52 Check Skills You’ll Need 10 -3
Area: Circles PRE-ALGEBRA LESSON 10 -3 Solutions 1. 3. 14 • 42 = 3. 14 • 4 = 50. 24 2. 3. 14 • 52 = 3. 14 • 5 = 78. 5 3. 3. 14 • 92 = 3. 14 • 9 = 254. 34 4. 3. 14 • 0. 52 = 3. 14 • 0. 5 = 0. 785 10 -3
Area: Circles PRE-ALGEBRA LESSON 10 -3 Find the exact area of a circle with diameter 20 in. A = = r 2 (10)2 = 100 The area is 100 r= 1 d; r = 10 2 Simplify. in. 2. Quick Check 10 -3
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. A = = r 2 (50)2 = 2, 500 (2, 500)(3. 14) = 7, 850 r= 1 d; r = 50 2 exact area Use 3. 14 for . approximate area The area of the region is about 7, 850 mi 2. Quick Check 10 -3
Area: Circles PRE-ALGEBRA LESSON 10 -3 A pound of grass seed covers approximately 675 ft 2. 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. Area of region that is one fourth of a circle: area of circle = r 2 1 area of quarter circle = 4 r 2 1 A (3. 14)(15)2 4 Replace = 176. 625 ft 2 10 -3 with 3. 14 and r with 15.
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 ft 2 The area of the lawn is about 177 ft 2 + 1, 125 ft 2 = 1, 302 ft 2. 1, 302 ÷ 675 1. 93 Divide to find the number of pounds of seed. You need to buy one 3 -lb bag of grass seed. 10 -3 Quick Check
Area: Circles PRE-ALGEBRA LESSON 10 -3 Find the area. 1. Find the exact area of a circle with diameter 32 in. 256 in. 2 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. 20 ft 2 b. What is the area of the rest of the room? Round to the nearest unit. 160 ft 2 10 -3
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