Question 1186084
<pre>
It falls down 20 meters, then up 10 meters.  So its first "down+up" is 30 meters.
Then it falls down 10 meters then up 5 meters. So its second "down+up" is 15
meters.  So we have an infinite geometric series with a<sub>1</sub> = first term = 30 and 
r = common ratio = 1/2.  The formula for the sum of any infinite geometric series
is:

{{{S[infinity]}}}{{{""=""}}}{{{a[1]/(1-r^"")}}}

Substituting:

{{{S[infinity]}}}{{{""=""}}}{{{30^""/(1-1/2)}}}{{{""=""}}}{{{30^""/(1/2)}}}{{{""=""}}}{{{30^""(2/1)}}}{{{""=""}}}{{{60}}}{{{meters}}}

Edwin</pre>