This is a crucial step in any type of statistical calculation, even if it is a simple figure like the mean or median.  Know how many numbers are in your sample. Do the numbers vary across a large range? Or are the differences between the numbers small, such as just a few decimal places? Know what type of data you are looking at. What do your numbers in your sample represent? this could be something like test scores, heart rate readings, height, weight etc. For example, a set of test scores is 10, 8, 10, 8, 8, and 4. You will need every number in your sample to calculate the mean.  The mean is the average of all your data points. This is calculated by adding all of the numbers in your sample, then dividing this figure by the how many numbers there are in your sample (n). In the sample of test scores (10, 8, 10, 8, 8, 4) there are 6 numbers in the sample. Therefore n = 6. This is the first part of calculating a mathematical average or mean.  For example, use the data set of quiz scores: 10, 8, 10, 8, 8, and 4. 10 + 8 + 10 + 8 + 8 + 4 = 48. This is the sum of all the numbers in the data set or sample. Add the numbers a second time to check your answer. This will provide the average or mean of the data.  In the sample of test scores (10, 8, 10, 8, 8, and 4) there are six numbers, so n = 6. The sum of the test scores in the example was 48. So you would divide 48 by n to figure out the mean. 48 / 6 = 8 The mean test score in the sample is 8.

TL;DR in Vietnamese:
Xem xét các số liệu. Tập hợp tất cả số liệu. Bước đầu tiên để tính giá trị trung bình là cộng dồn tất cả các giá trị bạn có trong bộ số liệu. Chia tổng trên cho số các số liệu (n).