Final answer:
The cousin probably measured the wall in feet, as inches and feet are both used to measure length, but represent different magnitudes. Measurements should be in the same unit to compare properly. Feet are generally more suitable for larger distances like walls.
Step-by-step explanation:
If you measure a wall and obtain a measurement of 9 inches, and your cousin measures the same wall and gets a measurement of 3, it is very likely that your cousin used a different unit of measurement, most probably feet. This can happen as both inches and feet are common units for measuring length, but they represent different magnitudes. An inch is a much smaller unit compared to a foot, which is equivalent to 12 inches.
To correctly compare measurements, they need to be in the same units. If the wall is actually 9 inches long, it would not make sense for it to be 3 feet long, as that would translate to 36 inches. It's crucial for both measurements to use the same unit to avoid confusion. The choice of measuring in feet or inches depends on the size of the wall; for larger measurements, like the length of a room, feet might be more appropriate.
When measuring objects or distances, it's essential to use units appropriate for the object's size. Meters, yards, and feet are suitable for longer distances, while inches, centimeters, and millimeters are better for smaller objects.