<image>Look at the picture and answer the following questions.
This semester, Class 4-1 launched a "mutual help and learning" activity. Here is Xiaoming's statistics chart of six math unit test scores this semester.

(1) Xiaoming's math test scores increased the fastest from the ____ test to the ____ test. (1 point)
(2) What is the average score of Xiaoming's six tests?
(3) Was this "mutual help and learning" activity useful? Why?