Can anyone help explain the following:

#141
Committee X and Committee Y, which have no common members, will combine to form Committee Z. Does Committee X have more members than Committee Y?

1) The average (arithmetic mean) age of the members of Committee X is 25.7 years and the average age of the members of Committee Y is 29.3 years.

2) The average (arithmetic mean) age of the members of Committee Z will be 26.6 years.