Assume there are approximately 5,000,000,000 (5 billion) people on Earth. What would you estimate to be the result, if you multiply together the number of fingers on every person left-hands? (For the purposes of this exercise, thumbs count as fingers, for five fingers per hand.) If you cannot estimate the number then try to guess how long the number would be ?

The product of the number of fingers on the left-hands of every person is zero. It only takes one person to have no fingers on their left hand for the product to be zero, because anything multiplied by zero equals zero.