Use the z-score formula to solve for the 98 percent confidence. The formula is z-score = (x - mean) / sigma.
In the formula, x is the data point, mean is the average of the numbers and sigma is the standard deviation of the numbers in your data set.
Find the z-value by plugging in the numbers. If x is 10, the mean is 5 and sigma is 2.3, then the z value is z = (10 - 5) / 2.3. Solving determines that z = 2.17.
After finding the z-value is 2.17, look up the conversion on a z-value table in a book or online. Using the table, it is learned that the z-value is 98.4996. This falls above the 98 percent confidence threshold that was set, so it is accepted. In other words, there is a 98 percent confidence that the number 10 could be found in the data.