SAT数学概率与统计习题回顾.

Averages are a statistics that are used to get information on a set of data.

The arithmetic mean of a set of n numbers is equal to the sum of the numbers divided by n. SAT math questions that use the word average rer to the arithmetic mean.

For example, the arithmetic mean of 4, 5 and 9 will be (4 + 5 + 9)/3 = 6.

Example of SAT question using the arithmetic mean: The average of the integers 24, 6, 12, x and y is 11. What is the value of the sum x + y?

(a) 11 (b) 17 (c) 13 (d) 15

• Answer: The average of the 5 numbers is (24 + 6 + 12 + x + y)/5. This should be equal to 11 according to the problem, so 24 + 6 + 12 + x + y = 11 · 5 = 55 x + y = 55 - 24 - 6 - 12 = 13

The median of a set of numbers is the number in the middle when the numbers are ordered. For example, the median of (1, 5, 2, 7, and 10) is 5 because when the numbers are ordered, 5 is in the middle. When there is an even number of values, the median is the same as the mean of the two middle numbers.