## gabbyalicorn one year ago The diameter of the larger circle is 12.5 cm. The diameter of the smaller circle is 3.5 cm. What is the approximate area of the shaded region? A. 28.26 cm² B. 113.04 cm² C. 132.27 cm² D. 254.34 cm²

1. gabbyalicorn

2. gabbyalicorn

I tried to get the answer by doing $12.5 \times 3.5 but \it turned out \to be 43.75 which was \not there. ;-; sadly$

3. gabbyalicorn

woah that was weird

4. gabbyalicorn

@gaos

5. gabbyalicorn

@pinklion23

6. gabbyalicorn

@Whitemonsterbunny17

7. gabbyalicorn

@geerky42

8. anonymous

Area of the greater circle- area of the smaller circle πRadius^2-πradius^2

9. gabbyalicorn

6.28

10. anonymous

3.14x(12.5)^2 - 3.13x(3.5)^2

11. geerky42

You just need to find area of big circle and small circle using $$A = \pi r^2$$ THEN you subtract big circle by small circle.

12. geerky42

First convert diameter into radius

13. gabbyalicorn

how do i do that?

14. geerky42

Let's just find area of bigger circle. diameter is 12.5 So what is radius?

15. gabbyalicorn

:/ radius is....a line segment that joins the center of a circle with any point on its circumference. (yes i looked it up)

16. geerky42

no no I mean what is length of radius in bigger circle?

17. gabbyalicorn

3.5

18. geerky42

Radius is 1/2 the diameter, right?

19. geerky42

So to find radius, you just divide diameter by 2

20. gabbyalicorn

yes

21. geerky42

So 12.5/2 = ?

22. gabbyalicorn

6.25

23. geerky42

Yeah, so now find area: $$A = \pi(6.25)^2$$

24. gabbyalicorn

39.25 i got kind confused on this part

25. geerky42

What are you confused with?

26. gabbyalicorn

just that whole part with the a= π(6.25.....etc thing

27. geerky42

$$\pi$$ is pi. You can use 3.14 for that. $$etc~^2$$ mean you multiply "etc" by itself For example $$4^2 = 4\times4$$

28. geerky42

Does that make sense?

29. gabbyalicorn

yes

30. geerky42

OK so $$A = \pi(6.25)^2$$ First, multiply 6.25 by itself

31. geerky42

Then multiply it by 3.14

32. gabbyalicorn

i got 122.6525

33. geerky42

Good enough. This is area of bigger circle. Keep that in mind. Now do it again, but with smaller circle (with diameter 3.5). Can you find area of smaller circle?

34. gabbyalicorn

so replace 6.25 with 3.5

35. geerky42

yeah basically.

36. gabbyalicorn

kk

37. gabbyalicorn

i got 38.465

38. geerky42

oops forgot to convert diameter into radius

39. geerky42

3.5 is diameter, so what is radius?

40. gabbyalicorn

um 12.5 ?

41. geerky42

No. To get radius, you divide diameter by 2.

42. geerky42

So 3.5/2 = ?

43. gabbyalicorn

oh 6.25

44. gabbyalicorn

I dont see it as the answer ;-; i think I did something wrong

45. geerky42

3.5/2 = ?

46. gabbyalicorn

1.75

47. gabbyalicorn

oh wow the online calculator was way off

48. geerky42

Yeah. so radius is 1.75. Now find area of circle.

49. geerky42

50. gabbyalicorn

1.75 x ? = ( 12.5 ) ?

51. geerky42

No. $$A = \pi(1.75)^2$$

52. gabbyalicorn

oh

53. gabbyalicorn

9.61625

54. gabbyalicorn

@geerky42

55. gabbyalicorn

i guess is didn't do it right. but i double checked and it still was this answer. HELP ;-;

56. gabbyalicorn

57. anonymous

find the area of the larg circle and the small circle

58. gabbyalicorn

12.5 is the area i belive

59. anonymous

no, that is the diameter

60. anonymous

remember, the area of a circle is $\pi r ^{2}$

61. anonymous

radius is half the diameter

62. gabbyalicorn

6.25

63. anonymous

yep, now plug it into the formula

64. gabbyalicorn

3.14 x 6.25 ?

65. gabbyalicorn

19.625

66. anonymous

6.25^2

67. gabbyalicorn

39.0625 ?

68. anonymous

don't forget about the pi

69. gabbyalicorn

122.65625

70. anonymous

yep, now find the area of the smaller circle

71. gabbyalicorn

um

72. gabbyalicorn

okay, so the smaller circle is 3.5

73. gabbyalicorn

so 3.14 a^2 ?

74. anonymous

3.5 is the diameter, what is the radius?

75. gabbyalicorn

6.25

76. anonymous

no its half the diameter

77. gabbyalicorn

3.125

78. anonymous

no what is the diameter of the smaller circle?

79. gabbyalicorn

3.5?

80. anonymous

yes, and the radius is half of that

81. gabbyalicorn

1.75

82. anonymous

now use the formula

83. gabbyalicorn

9.61625

84. anonymous

correct

85. anonymous

now subtract the area of the small circle from the large circle

86. gabbyalicorn

113.03625

87. anonymous

good job

88. gabbyalicorn

so, b

89. gabbyalicorn

:D yay! thank you for helping me!

90. anonymous

np