Answer: Exponential decay function
Explanation:
Given: Each day 1/2 the money that is in the bank vault is removed. no money is added to the vault.
The constant ratio of decay =

- A function is said to be exponential decay function if it decreases at a rate proportional to its previous value.
Here the amount in the bank is decreasing at a constant ratio of
.
Therefore, the exponential decay function models the situation.