HP 20b Using the RPN stack to solve problems efficiently
This solution works on all RPN-calculators I know but gives -0.91 on HP 20b instead. The reason is that +/- copies register X to ANS. Thus the 2nd ANS returns 1/x instead of x.
Microchallenge: Can you help HP and find the correct sequence?
Here's the link to get all HP 20b Training Modules.