Relation between diameter and circumference

The relation between the circumference of an electron orbit in a hydrogen atom and the de broglie wavelength of the electron in the same orbit is given by

If the difference between the outer radius and the inner radius of a ring is 14 cm, then what is the difference between is outer circumference and innner circumference?

The ratio of the area and circumference of a circle of diameter d is d(b)(d)/(2)(d)/(4)(d)2d

The ratio of the perimeter (circumference) and diameter of a circle is pi( b) 2 pi(pi)/(2) (d) (pi)/(4)

If the difference between the circumference and diameter of a circle is 30 cm, then what is the radius of the circle ?

The difference between the circumference and the diameter of the circle is 15 m . What is the area of the circle ?

The differences between the circumference and diameter of a circle is 60 cm, then radius is

If the difference between the circumference and diameter of a circle is 30 cm, then the radius of the circle must be