deletions | additions       diff --git a/The Earth.tex b/The Earth.tex  index 840b908..d5fb3d0 100644  --- a/The Earth.tex  +++ b/The Earth.tex 
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\begin{enumerate}  \item {\it What is the radius of the Earth?}  My most recent frequent-flyer statement says that there are 3000 miles from Boston (BOS) to Los Angeles (LAX). Since planes travel along great circles, this distance $D_{\rm US}$ represents a segment of the Earth's circumference. There are four time zones (three intervals) from Boston to Los Angeles, out of 24, so $D_{\rm US}$ represents 1/8 of the Earth's circumference.     \begin{align}   \label{cearth}   C_\oplus = 8 D_{\rm US} &= 2\pi R_\oplus \nonumber \\   R_\oplus &= \frac{8 D_{\rm US}}{2 \pi}   \end{align}  \item {\it What is the mass of the Earth?}  \end{enumerate}