Answer:  [C]:  "Each circle has only one diameter."
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Answer:
Percentage decrease = 10% × 0.82 
New value = 0.82 - Percentage decrease
Let me know if this helps! :)
 
        
             
        
        
        
The answer is ten if I'm correct
        
                    
             
        
        
        
The answer is C) 160. 
We know this because if mA = 50, we know that mC must also be 50. This is due to the fact that AB = BC. This leaves us with mB as 80 since the angles of a triangle always have to equal 180. 
Now knowing this, it is easy to find the arc lengths in degrees. When you have a transcribed triangle, all we are going to do here is double the angle of the triangle to get the arc measure. 
mB = 80
80*2 = 160