Final answer:
Anna is using a ruler to estimate the height of a tree by visually aligning it so the tree height is covered by it. A measuring tape is typically used for such measurements to provide length in feet or yards. However, Anna uses her ruler and estimation skills to approximate the tree's height.
Step-by-step explanation:
Anna is estimating the height of a tree by using a method that involves comparing one relatively known measurement to an unknown measurement. In this instance, she uses a ruler as her measurement reference, and she visually aligns it so the height of the tree is exactly covered by the ruler. This practical approach is based on the concept that one can get big lengths from smaller lengths by breaking down a larger object into smaller, more manageable units.
The ideal measuring tool for tasks such as this depends on the object's size. Since the height of a tree can be several feet tall, a measuring tape would typically be used for such measurements because it can be extended to measure greater lengths in appropriate units like feet or yards.
However, in the case where only a ruler is available and one needs to create an estimate, imagination and approximation skills come into play. By covering the height of the tree with a small ruler, Anna may estimate the height by considering how many times the ruler's length would stack up to reach the top of the tree, thereby multiplying the length of the ruler by this number to estimate the overall height of the tree.