Problem: Indicate which of the following are exact numbers.(a) the mass of a 32-oz can of coffee(b) the number of students in your chemistry class(c) the temperature of the surface of the Sun(d) the mass of a postage stamp(e) the number of milliliters in a cubic meter of water(f) the average height of NBA basketball players

Recall that Exact numbers are either defined numbers or the result of a count. 

• Examples of exact numbers are the following:
  • Conversions within the American system (such as pounds to ounces, the number of feet in a mile, the number of inches in a foot, etc).
  • Conversions with the metric system (such as kilograms to grams, the number of meters in a kilometer, the number of centimeters in a meter).
  • The words per and percent mean exactly out of one or one hundred, respectively.
  • Counted numbers are exact: there are two chairs in the photograph. There are fifteen books on the shelf. Eighty-seven people attended the lecture.

An exact number can only be expressed in one way and cannot be simplified any further. Exact numbers have an infinite number of significant figures, but they often appear as integers.