The arithmetic mean (average) of a set of numbers is calculated by adding all the numbers together and then dividing by the total number of values.

Given the numbers: 105, 165, 144, 103, 113

1. Add the numbers together: $105 + 165 + 144 + 103 + 113 = 630$

2. Divide the sum by the number of values (5): $\frac{630}{5} = 126$

Thus, the arithmetic mean is 126.

Would you like further details or have any questions?

Here are 5 related questions for further practice:

1. What is the arithmetic mean of 50, 75, 100, 125, and 150?
2. How would the mean change if you added a new number, say 200, to the set?
3. What is the median of the numbers 105, 165, 144, 103, and 113?
4. Can the arithmetic mean of a set of numbers ever be smaller than all the individual values in the set?
5. How does the arithmetic mean compare to the mode for this data set?

Tip: The arithmetic mean is sensitive to outliers (extremely high or low values) in the data set.