Diagrams and Sketches

Some problems involve the determination of a quantity of items, such as the number of nails per sheet of plywood or the number of studs in a wall. In solving these types of problems it usually is helpful to draw a sketch or a diagram.

Problem: How many posts are needed to build a fence 100 ft long with posts 10 ft apart?

Solution: For many people the first response would be 10:

100 ft

10.0 ft/post but a diagram, Figure 1.1 shows that the correct number of posts is 11.

This is an example of a situation where a wrong answer is possible if you do not interpret the problem correctly. In this example, 10 is the number of spaces, not the number of posts.

FIGURE 1.1. Number of posts.

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