Answer: The inner diameter of the ring is 16 mm.
Step-by-step explanation:
As we know that ,
Circumference of a circle = [tex]\pi d[/tex] , where d = diameter of the circle .
We are given that ,
The circumference of the outside of a ring is 66 mm and it has an outer diameter of 21 mm .
Now , if circumference of the inside the ring is 50 mm, then we have
[tex]50 = \pi d[/tex] , where d= diameter of the inner circle .
Then , [tex]d=\dfrac{50}{\pi}=\dfrac{50}{\dfrac{22}{7}}=\dfrac{50\times7}{22}\approx15.909090909\approx16\text{ mm}[/tex]
Hence , the inner diameter of the ring is 16 mm.
