#### Answer

The concept of "counting by weighing" is used when counting extremely large quantities of an object such as marbles. For example, counting out 1 million marbles will take many hours of work. However, if we knew the weight of a marble, we can find how much 1 million marbles would weigh and measure out that weight which should be 1 million marbles.

#### Work Step by Step

The concept of "counting by weighing" is an alternative method of counting large numbers of objects using their average weight. For example, if we were to count out 1 million marbles individually, it would take many hours. However, if we knew the mass of one marble, we could quickly measure out one million marbles by the weight of one million marbles.