On August 21 2009 the World Health Organization announced its prediction that the number of new cases of H1N1 (swine flu) virus would double every 5 days for several months. As of July 27 2009 the number of new cases was 26116. Which one of the following exponential functions model the growth of this virus?

Question

Quizplus · Accepted Answer

The exponential function that models this situation is of the form $y=a \cdot b^x$, where $y$ is the number of cases and $x$ is the number of 5-day intervals that have passed since July 27, 2009. We know that the number of cases doubles every 5 days, so $b=2$. We can find $a$ by plugging in the initial value at $x=0$:

$26116=a \cdot 2^0$
$a=26116$

Therefore, the function that models the growth of the virus is $y=26116 \cdot 2^x$.

Choice (B) is the only option with the correct base of 2 and initial value of 26116. The other choices either have a different base or an incorrect initial value.

On August 21 2009 the World Health Organization Announced Its