Remember that the general decay equation is:
where
is the amount after a time 
is the initial amount
is the the decay percent in decimal form
The first ting we are going to do is find by dividing our <span>decay rate of 25% by 100%: </span>
.
We also know from our problem that
. Lets replace and in our formula:
We know now that our decay rate is 0.75, and since 0.75<1, we can conclude that this situation represents exponential decay.
Now, to find the initial amount, we are going to solve our equation for
:
Notice that will depend on the number of ours . <span />
where
The first ting we are going to do is find
We also know from our problem that
We know now that our decay rate is 0.75, and since 0.75<1, we can conclude that this situation represents exponential decay.
Now, to find the initial amount, we are going to solve our equation for
Notice that