Given, first three multiples of 5 are: 5, 10, 15.
Sum of observations = 5 + 10 + 15 = 30
Number of observations = 3
Arithmetic mean = \(\frac {Sum\,of\,observations}{Number\,of\,observations}\) = 30/3 = 10
∴ Arithmetic mean of first three multiples of 5 is 10.
