Question 3998
if you look at the sequence:

to get from 9 to 6: you have to multiply by 2/3.
Now you aren't sure if that is the mean operation you have to do. 
To be sure: just check on the other numbers if you are at the right end:

And yes: 6*(2/3)=4 ; 4*(2/3)=8/3.

So the next term in the sequence will be (8/3)*(2/3)=16/9.

This is an example of a GEOMETRIC SEQUENCE. 

Greets, Pieter