Find the arithmetic mean of the first 7 multiples of 7.

The first 7 multiples of 7 are 7, 14, 21, 28, 35, 42 and 49.

Sum of the first 7 multiples 

= 7 + 14 + 21 + 28 + 35 + 42 + 49

= 196

No. of observations = 7

∴ Arithmetic Mean of the first 7 multiples = $\frac{196}{7} = 28$

Thus, the arithmetic mean of the first 7 multiples of 7 is 28.