How Many?

At work this week is our Jewson charity challenge . We are trying to raise money for our chosen charity which this year is We Are Macmillan . One of the things we have done is to put a Jar of gravel on the counter and are charging people to have a guess as to how many pieces of gravel are in the jar with chance to win a circular saw.
No one knows how many are in the jar someone will have the job of counting it out after the competition closes . We gave the job of filling the jar to our management trainee who we then found picking all the gravel out of a bag of ballast mixed with sand instead of going to the bag of just gravel he will go far