Answer
$1$
Work Step by Step
Using the fact that $\frac{u'}{u}=\ln u $, we have
$$\int_1^{e} \frac{1}{x}dx =\ln x|_1^{e}=\ln e-\ln 1=1. $$
where used the properties $\ln e=1$ and $\ln 1=0$.
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