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Area For this course, area is the number of square units needed to fill up a region on a flat surface. In later courses, the idea will be extended to cones, spheres, and more complex surfaces. Also see surface area. Compound Event A compound event in probability is an outcome that depends on two or more other events. For example, finding the probability that both a red ball and also a blue block are drawn from a bag in two draws. Desired Outcome In the context of probability, “successful” usually means a desired or specified outcome (event), such as rolling a 2 on a number cube (probability of ). Equivalent Fractions Two fractions are equivalent if they have the same numerical value. For example, 3/6 and 5/10 are equivalent fractions. Experimental Probability The probability based on data collected in experiments. The experimental probability of an event is defined to be . Lowest Common Denominator The smallest common multiple of the denominators of two or more fractions. For example, the LCD of and is 24. Interval A set of numbers between two given numbers. Mean The mean, or average, of several numbers is one way of defining the “middle” of the numbers. To find the average of a group of numbers, add the numbers together then divide by the number of numbers in the set. For example, the average of the numbers 1, 5, and 6 is (1 + 5 + 6) ÷ 3 = 4. The mean is generally the best measure of central tendency when there are not outliers in the data set. See average. Measure of Central Tendency Mean, median, and mode are all measures of central tendency, reflecting special statistical information about a set of data. See center of a data distribution. Median The middle number of an ordered set of data. If there is no distinct middle, then the average of the two middle numbers is the median. The median is generally more accurate than the mean as a measure of central tendency when there are outliers in the data set. Multiplicative Identity The multiplicative identity property states that multiplying any expression by 1 leaves the expression unchanged. That is, a(1) = a. For example, 437 x · 1 = 437x. Outcome Possible result in an experiment or consequence of an action. Outlier A number in a set of data that is much larger or much smaller than the other numbers in the set. Parallelogram A quadrilateral with two pairs of parallel sides. Percent (%) A ratio that compares a number to 100. Percents are often written using the “%” symbol. For example, 0.75 is equal to or 75%. Perimeter The distance around a figure on a flat surface. Possible Outcomes In the context of probability, outcomes with any chance of happening. Probability A number that represents how likely an event is to happen. When a event has a finite number of equally-likely outcomes, the probability that one of those outcomes, called A, will occur is expressed as a ratio and written as: . For example, when flipping a coin, the probability of getting tails, P(tails), is 1/2 because there is only one tail (successful outcome) out of the two possible equally likely outcomes (a head and a tail). Probability may be written as a ratio, decimal, or percent. A probability of 0 (or 0%) indicates that the occurrence of that outcome is impossible, while a probability of 1 (or 100%) indicates that the event must occur. Events that “might happen” will have values somewhere between 0 and 1 (or between 0% and 100%). Proportional Relationship Two values are in a proportional relationship if a proportion may be set up that relates the values. Rectangle A quadrilateral with four right angles. Repeating Decimals A repeating decimal is a decimal that repeats the same sequence of digits forever from some point onward. For example, 4.56073073073… is a decimal for which the three digits 073 continue to repeat forever. Repeating decimals are always the decimal expansions of rational numbers. Sample Space The collection of all possible outcomes of an event. Scaling (scale) The ratio between a length of the representation (such as a map, model, or diagram) and the corresponding length of the actual object. For example, the map of a city may use one inch to represent one mile. Terminating Decimal A terminating decimal is a decimal that has only a finite number of non-zero digits, such as 4.067. Terminating decimals are a particular kind of repeating decimal for which the repeating portion is zeros, so the example could be written 4.0670000000… but it is not necessary to write the zeros at the end. Theoretical Probability A calculated probability based on the possible outcomes when each outcome has the same chance of occurring: (number of successful outcomes)/(total number of possible outcomes). Trapezoid A quadrilateral with at least one pair of parallel sides. Triangle A polygon with three sides.