U

undefined

Division by 0 is undefined because there is no number that satisfies the definition of division when 0 is the divisor. For example, if there were a number n = 3 ÷ 0, it would be the unique number n that makes n 0 = 3 a true statement. There is no such n.

pages 217–218

unit of measurement

A precisely fixed quantity used to measure; centimeter, foot, kilogram, and quart are units of measurement.

unit whole

The shape or piece that is equal to 1.

pages 311, 320–331, 332–336, 456, 464

unknown

3072 = 3000 + n + 2. The n is called an unknown.

pages 125–126

using simpler numbers

A strategy of using easier numbers to make solving a problem simpler.

page 162