3. find the diameter of a circle with a circumference of 50 mm. round your answer to the nearest tenth.
16.0 mm
26.4 mm
8.4 mm
33.5 mm

1) Equation that you need is: 

C = 2πr 

The diagram shows that the radius is 3.5, so plug it in the equation and solve for C 

C = 2(3.14)(3.5) 
C = 21.98 
Rounded to tenth: 22.0 

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2) The equation you need to know here is: 

A = πr² 

The diagram shows diameter is 12, so radius is 6. Plus in the info, we have and solve for A 

A = 3.14(6)² 
A = 113.04 
rounded to tenths: 113.0 

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3) Find the diameter of a circle with a circumference of 50mm. 

C = 2πr 
50 = 2(3.14)r 
50 = 6.28r 
r = 50 / 6.28 
r = 7.96 

You were asked to find the diameter, so double that, then round it to tenths: 

d = 2r 
d = 2(7.96) 
d = 15.92 
Rounded to 15.9mm