What is the circumference (in fractions of an inch) of a circle whose diameter is five eighths of an inch?

What's the formula for circumference?

The definition of the special number "pi" is the ratio of a circle's circumference to its diameter. Consequently the circumference of the circle is equal to pi times the diameter. You say the answer should be given in "fractions of an inch" - have they given you a value to use for pi ? Although pi cannot be expressed as a fraction itself, one commonly used approximation for it is 22/7. So this problem boils down to multiplying 5/8 x 22/7.