The circumference of a circle is 5.2mm find the length of the diameter rounded to 3sf

Consider the equation for the circumference of a circle, 2πr. Notice that this can also be written as 2rπ.

Recall that the diameter of a circle is equal to twice the radius, or

d = 2r

And make a substitution into the original equation, giving us the circumference c = πd. We know the circumference is 5.2mm; plugging in, we get

5.2 = πd.

Note: π is NOT a variable, it represents a number. Therefore, we can solve the equation for the diameter d = c / π, or

d = 5.2 / π.

I'll let you crunch the number :D

I hope this helps!