20. A scientist is walking through a forest, and she records the heights of 5 trees in a row using integers. She notices that the height of each tree is either twice or half the height of the tree to its right. Unfortunately, due to the rain, some of her data is lost, where the dashes represent the missing data (as shown in Table 1). Based on her observations, she can re-determine these numbers. What is the average height of these trees?
Table 1
\begin{tabular}{|l|r|}
\hline First tree & meters \\
Second tree & 11 meters \\
Third tree & meters \\
Fourth tree & meters \\
Fifth tree & meters \\
\hline Average height & .2 meters \\
\hline
\end{tabular}
) meters.
(A) 22.2
(B) 24.2
(C) 33.2
(D) 35.2
(E) 37.2
20. B.

Notice that, the height of each tree is an integer.
Given that the height of the second tree is 11 meters, the sum of the heights of the first and third trees must be 22 meters.
Now consider the height of the fourth tree.
It cannot be 11 meters, otherwise, the fifth tree would have to be 22 meters, and thus, the average of the sum of the heights of the five trees would not end in 0.2.

Therefore, the height of the fourth tree is 44 meters. At this point, the sum of the heights of the first four trees is 99, so the height of the fifth tree cannot be 88, but must be 22 meters.
Thus, the average height of the five trees is
$$
\frac{22+99}{5}=\frac{121}{5}=24.2 \text { (meters). }
$$