Question

The circumference of a circle varies directly as the diameter of a circle. When the diameter of a circle is 5, the circumference of the circle is approximately 15.7.

What is the approximate circumference of a circle with a diameter of 9? Round answer to nearest tenth.



2.9

8.7

28.3

706.5

Answer 1

@kevinngo

Answer 2

Well we know the circumference of a circle is 2*pi*r
where r=radius the radius is half the diameter
So If the diameter is 9 then the radius is 9/2=4.5
So then circumference of the circle is 2*pi*4.5 or in other words pi*9 = 28.27
which can be rounded to 28.3

Answer 3

we can use proportions if we would like since we have another circle to compare to