Answer
$48$ years old.
Work Step by Step
Let $P(x)=50$; we have
$\frac{90}{1+271e^{-0.122x}}=50$
and
$271e^{-0.122x}=\frac{90}{50}-1=0.8$
Thus
$x=-\frac{ln(0.8/271)}{0.122}\approx48$ years old.
Precalculus (6th Edition) Blitzer
by Blitzer, Robert F.
Published by
Pearson
ISBN 10:
0-13446-914-3
ISBN 13:
978-0-13446-914-0
Chapter 3 - Section 3.5 - Exponential Growth and Decay; Modeling Data - Exercise Set - Page 507: 45
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