سؤال قراءة ستيب محلول — فهم التفاصيل (تدريب 7021)

(1) Statistics is a branch of mathematics. It involves gathering information and summarizing it. The numbers that result from this work are also called statistics. They can help to predict such things as the weather and how sports teams will perform. They also can describe specific things about large groups of people- for example, the reading level of students, the opinions of voters, or the average weight of a city’s residents. (2) The people who gather statistics are called statisticians. They collect pieces of information, or data, in three basic ways. They refer to trustworthy sources, such as newspapers and reports from reliable organizations. They perform scientific experiments. They also conduct surveys, or ask people questions. (3) Sometimes statisticians cannot gather data about every member of a group, often because the group is too large. In such cases they study only part of the group, called a sample. A sample must accurately represent the larger population. For example, if women make up 60 percent of the population, then 60 percent of the sample must be women. (4) Once statisticians have collected their information, they summarize it. They often put the data in graphs or charts, which are easier to read than long lists of data. Statisticians also summarize data by calculating numbers called averages. There are three kinds of averages: mean, mode, and median. The mean is the sum of a set of numbers divided by the number of elements in the set. The mode is simply the number that occurs most often in a sample. The median is the number right in the middle of the sample. What is one important idea related to collecting data from a sample from