Question 271029
The formula for circumference is
{{{C = 2*pi*r}}}
From above , we get
{{{25 = 2*pi*r}}}
dividing by 2pi, we get
{{{25/(2*pi) = r}}}
This means that 
{{{r = 3.979}}} inches and the diameter is
{{{d = 7.958}}} inches