1. + Bell Work Solve 25 ⅚ -18 ⅜ 5 ⅛ + 7 ⅘

2. + Bell Work Answer 25 ⅚ -18 ⅜ 25 20/24 – 18 9/24 7 11/24 5 ⅛ + 7 ⅘ 5 5/40 + 7 32/40 12 37/40

3. + Lesson 3: Perimeter and Circumference

4. + What is a perimeter?

5. + Perimeter* The distance around an object.

6. + Find the perimeter of this object

7. + Answer: 28 Units

8. + Find the perimeter of the object

9. + Answer: 44 Units

10. + Every point on a circle is the same distance from the center of the circle. This distance is called the radius. Radius*: The straight line from the center of the circle to the outer edge.

11. + Diameter*: Twice the length of the radius of a circle.

12. + Circumference*: The perimeter of a circle.

13. + Many ancients thought that the circle was the perfect geometric figure. They were especially interested in the relationship between the diameter of a circle and the circumference of the same circle. They found that it takes approximately 3.14 diameters to go all the way around a circle no matter how small or large the circle is.

14. + We now know the exact number of times the diameter will go around a circle. This exact number is a number is a number we call pi (pronounced pie). We represent pi with the symbol π.

15. + π is an infinite number meaning that it will go on and on forever. This also means that it is an irrational number. A calculator gives a decimal approximation of π as 3.141592654. (In the book, 3.14 will be used as an approximation for pi when doing calculations.)

16. + It takes π diameters to equal the circumference of a circle. Circumference = πD

17. + It takes 2π radii to equal the circumference of a circle. Circumference = 2πr

18. + Example: The radius of a circle is 3 cm. Find the circumference of the circle.

19. + Answer: Circumference = 2πr = 2π(3 cm) = 2(3.14)(3 cm) = 18.84 cm

20. + Example: The circumference of a circle is 24 meters. Find the radius of the circle.

21. + Answer: Circumference = 2πr 24 m = 2πr 24 m = 2(3.14)(r) 24 m = 6.28r r = 3.82m

22. + Find the perimeter of the figure

23. + Answer: Perimeter = 10 ft +10 ft + 8 ft + (2π(4 ft)/2) = 28 ft + (2(3.14)(4 ft)/2) = 28 ft + 12.56 ft = 40.56 ft

24. + Practice: The length of a rectangle is 10 cm. The width of the rectangle is 5 cm. Find the perimeter of the rectangle.

25. + Practice: The perimeter of a square is 12 meters. What is the length of one side of the square?

26. + Practice: The radius of a circle is 5 inches. Find the circumference of the circle.

27. + HW: Lesson 3 #1-30 Due Tomorrow