__O__

**Obtuse angle ** An
angle with measure between 90°
and 180°.

**Obtuse triangle ** A
triangle that has one obtuse angle.

**Odds** A ratio that compares the probability of an event occurring and
the probability of the event not occurring.

**Open sentence ** A
mathematical sentence that contains one or more variables.

opposite
of such a fraction.

**Opposites ** A pair
of numbers such as - and .

**Order
of operations **The rules
stating the order to follow in working a problem containing several different
operations

**Ordered pair of numbers ** A
pair of numbers whose order is important.

**Ordering
**Arranging
a set of numbers in a list so that each number is less than the numbers that
come after it in the

list
and greater than the numbers that come before it

**Origin ** ,
The graph of zero on a number line or in a rectangular coordinate plane.

**Outcome ** The
result of an event.