Problem 22
The smaller inner circle has a radius of r = 5. That will be plugged into the circumference formula below.
C = 2pi*r
C = 2pi*5
C = 10pi
This is the exact distance around the circle in terms of pi. Think of it like the amount of fencing you need to enclose the circle.
If you want an approximate perimeter, then use something like pi = 3.14
So 10pi = 10*3.14 = 31.4 cm is the approximate perimeter aka circumference of the smaller circle.
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The larger circle is the same idea. The radius is r = 5+5 = 10 cm
C = 2pi*r
C = 2pi*10
C = 20pi .... exact circumference
C = 20*3.14
C = 62.8 ... approximate circumference
Use more decimal digits of pi to get a more accurate value.
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Problem 23
The smaller circle has a diameter of 9 ft, which means the radius is r = 9/2 = 4.5 ft
C = 2pi*r
C = 2pi*4.5
C = 9pi .... exact circumference
C = 9*3.14
C = 28.26 .... approximate circumference
The units of the circumference are in feet
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The larger circle has radius r = 4.5+2.5 = 7 ft
C = 2pi*r
C = 2pi*7
C = 14pi .... exact circumference
C = 14*3.14
C = 43.96 .... approximate circumference
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Problem 24
The larger circle has radius 22. This radius is the diameter of the smaller circle.
So the smaller circle has radius 22/2 = 11
C = 2pi*r
C = 2pi*11
C = 11pi .... exact circumference
C = 11*3.14
C = 34.54 .... approximate circumference
The circumference units are "meters".
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Now onto the larger circle
C = 2pi*r
C = 2pi*22
C = 44pi .... exact circumference
C = 44*3.14
C = 138.16 .... approximate circumference