An inequality tells us that one value is *less than* or *greater than* another value.

Suppose we knew the temperature is *less than *$3^\circ \text{F}$, but we don’t know exactly what it is. To represent what we know about the temperature $t$ in $^\circ \text{F}$ we can write the inequality: $$t< 3$$

The temperature can also be graphed on a number line. Any point to the left of 3 is a possible value for $t$. The open circle at 3 means that $t$ cannot be *equal* to 3, because the temperature is *less than *3.

Here is another example. Suppose a young traveler has to be at least 16 years old to fly on an airplane without an accompanying adult.

If $a$ represents the age of the traveler, any number greater than 16 is a possible value for $a$, and 16 itself is also a possible value of $a$. We can show this on a number line by drawing a closed circle at 16 to show that it meets the requirement (a 16-year-old person can travel alone). From there, we draw a line that points to the right.

We can also write an inequality and equation to show possible values for $a$: $$a>16$$ $$a=16$$