An obtuse angle is bigger than 90° but smaller than 180°.

An odd number is an integer that is not divisible by 2. The odd numbers are -5,-3,-1, 1, 3, 5.

Operation is the process of combining numbers or expressions. In the primary years, operations include addition, subtraction, multiplication, and division. In later years, operations include, for instance, raising to a power, taking the logarithm, and more complex operations, such as integration.

Order of operations refers to a collection of rules for simplifying expressions. It stipulates that calculations in brackets must be made first, followed by calculations involving indices (powers, exponents), then multiplication and division (working from left to right), and lastly, addition and subtraction (also in order from left to right); for example, in 5-6÷2+7, the division is performed first and the expression becomes 5-3+7=9. If the convention is ignored and the operations are performed in the order they are written, the incorrect result, 6.5 is obtained.

In mathematics, an ordered pair is a collection of two numbers whose order is significant. Ordered pairs are used to describe the location of a point in the Cartesian plane.

An outlier is a data value that appears to stand out from the other members of the data set by being unusually high or low. The most effective way of identifying outliers in a data set is to graph the data; for example, in the following list of ages of a group of 10 people, {12, 12, 13, 13, 13, 13, 13, 14, 14, 14, 24}, the number 24 would be considered to be a possible outlier.