20 inch
You can invent any number of nonstandard units, but none of them is "best". It is best to use standard units, that is, the meter.
4-5 1/2 meters
An inch is roughly equivalent to the width of an adult thumb, but this can vary from person to person. Typically, many people find that their thumb is about 1 inch wide, making it a useful informal measurement. However, for precise measurements, it's best to use a ruler or measuring tape.
Whole numbers are the best representation of students.
Measurement error: obviously!
Well, sweetheart, the best estimate for the width of a classroom would typically be around 20 to 25 feet wide. But hey, if you want to get fancy with it, you can always whip out a measuring tape and get the exact number. Just make sure to watch out for any lurking dust bunnies while you're at it.
Answer: meters
200mm
The best measurement for a phonebook would be its dimensions, typically expressed in height, width, and thickness. This provides a clear understanding of the physical size of the phonebook.
A millimetre.
milimeters
9 cm
You can invent any number of nonstandard units, but none of them is "best". It is best to use standard units, that is, the meter.
It's Yard
in miles
The metric measurement that is the best estimate for the length of a car is typically in meters or centimeters. This allows for a more precise measurement compared to using larger units such as kilometers.
Inches or centimeters.