Question 1111662
60, 30, 20, 15, 12.5, 11.25, ...
 
The first differences for 60, 30, 20, 15 are
60 - 30 = 20,
30 - 20 = 10,
20 - 15 = 5
Each difference is half of the difference before.
The next differences would be
{{{5/2=2.5}}} ,
{{{2.5/2=1.25}}} , etc.
so, the next two terms are
{{{15-2.5=12.5}}} and {{{12.5-1.25=11.25}}} .