January 22nd, 2017, 01:14 PM  #1 
Newbie Joined: Jan 2017 From: cullowhee Posts: 1 Thanks: 0  question about exponential formula
A population, P(t) (in millions) in year t, increases exponentially. Suppose P(9)=20 and P(eighteen)=29. a) Find a formula for the population in the form P(t)=ab^t Enter the values you found for a and b in your formula in the blanks below. Round your values to 4 decimal places. a= b= 
January 22nd, 2017, 01:52 PM  #2  
Math Team Joined: May 2013 From: The Astral plane Posts: 2,306 Thanks: 964 Math Focus: Wibbly wobbly timeywimey stuff.  Quote:
$\displaystyle P(9) = ab^9 = 20$ $\displaystyle P(18 ) = ab^{18} = 29$ Now divide: $\displaystyle \frac{ \text{P}(18 )}{ \text{P}(9) } = \frac{a b^{18} }{ a b^9} = \frac{29}{20}$ $\displaystyle b^9 = \frac{29}{20}$ Now you can find b. See what you can do from here to find a. Dan  

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