Question 961170
<pre>
If it were arithmetic, then

{{{2/30-1/20 = 3/40-2/30 = 4/50-3/40}}} or

{{{cross(1/60 = 1/120 = 1/200)}}}

That's certainly false.

If it were geometric, then

{{{(2/30)/(1/20) = (3/40)/(2/30) = (4/50)/(3/40)}}} or

{{{cross(4/3 = 9/8 = 16/15)}}}

That's certainly false.

So it's neither.

Edwin</pre>