One thousand-millionth of a metre
(1×10−9 m = 0.000 000 001 m).
One thousand-millionth of a second
(10−9 s = 0.000 000 001 s).
Each positive whole number has a negative counterpart, an equal distance from zero but on the opposite side of the number line. Negative numbers are sometimes called directed numbers as they add a sense of direction as well as magnitude (e.g. temperatures below 0° C).
A number sentence is typically a statement of equality or inequality using numbers and common symbols. For example: 8 + 5 = 13 and 16 - ☐ = 10 are both number sentences.