Sigma Notation and Calculating the Arithmetic Mean · Exercise 1

A group of 10 children are on a scavenger hunt to find different color rocks. The results are shown in the below. The column on the right shows the number of colors of rocks each child has. What is the mean number of rocks?
$$\begin{array}{cc}\text{Child}& \text{Rock colors}\\ \text{1}& \text{5}\\ \text{2}& \text{5}\\ \text{3}& \text{6}\\ \text{4}& \text{2}\\ \text{5}& \text{4}\\ \text{6}& \text{3}\\ \text{7}& \text{7}\\ \text{8}& \text{2}\\ \text{9}& \text{1}\\ \text{10}& \text{10}\end{array}$$

Its source prints no answer for this problem, so there's nothing to check against.

OpenStax, Introductory Business Statistics 2e · §2.4 Sigma Notation and Calculating the Arithmetic Mean · Exercise 1