Given number are 3, 6, 9, 12, 15
Arithmetic Mean
If mean is increased by 2 then,
9 + 2
= \(\frac{Sum\,of\,observation}{5}\)
Sum of observations = 5 x 11
= 55
Difference in sum = 55 – 45
= 10
∴ Each number is increased by 2 if the mean is increased by 2.