<p>4.7 was the agreed upon answer</p>
<p>Do you guys know if all the tests were the same?</p>
<p>everyone else says 24 weeks</p>
<p>kdines
21 is what you get if you use only two of the three points given (specifically, (0, 400) and (5, 850)–and not (10, 1520)) and get the exponential equation by hand from them. You’d have gotten the equation y = a<em>b^x, where a = 400 and b = 2.125^(1/5)) = 1.1627110105. Solving a</em>b^x = 10,000 would then give you approx. 21.</p>
<p>However, the problem asked to use an exponential regression to get the equation y=a<em>b^x. When you input all three points in L1 and L2 and then ask your TI for an exp. regression, you get a = 411.6698… and b = 1.142821… Solving a</em>b^x = 10,000 with this a and b gives you approx. 24.</p>
<p>If it were possible to find an equation of the form y = a<em>b^x with all three points on it, then both methods would give the same answer, but it’s not possible. Your equation, for example does not go through the third point: if you plug in x=10 into your equation (y = 400</em>1.1627110105^x), you don’t get 1520, but 1806. The exponential regression equation the TI gives, doesn’t go through any of the three points, but it’s the “closest fit” to them.</p>