SOLUTION: I need an exponential decay growth for this problem: The first cleaning takes you 135 minutes. You notice that for each cleaning after that, you decrease the time it takes from

Question 446950: I need an exponential decay growth for this problem:
The first cleaning takes you 135 minutes. You notice that for each cleaning after that, you decrease the time it takes from the week before by one-fifth. I need to deterine the function to model.
I'm thinking it is y=(1/5)^x, but I'm not sure.
Thanks for your help.
Answer by htmentor(1343) (Show Source): You can put this solution on YOUR website!
If each successive time is reduced by 1/5, that means that the current week's
time is 4/5 the time of the previous week.
Let x = the number of weeks after the 1st week, y = the cleaning time.
Since the initial time is 135 min. we can express the time for a given week as:

For the 1st week, x=0, so y = 135 min.
For the 2nd week, x=1, so y = (4/5)135 = 108 min., etc.
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