There are $n$ jellybeans in a bottle with unknown dimensions. What is the only surefire way of knowing how many jellybeans are in the bottle?
There is another way that is probably far less time-consuming, depending on $n$.
Weigh the bottle of jellybeans. Call this value $F$.
Pour out the bottle of jellybeans.
Weigh the empty bottle. Call this value $E$.
Weigh a single jellybean. Call this value $J$.
The number of jellybeans is