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.

                                                                                                   

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