Hello
Yesterday I was playing around with the Tolerances package in Maple 12. To familiarize myself I with it I tried to work out the equivalent resistance of two parallel resistors with tolerances.
R1:=80.0 +/- 4.0 [Ohm]
R2:=120.0 +/- 6.0 [Ohm]
Maple returned: Req:=R1*R2/(R1+R2) = 48.5 +/- 7.22 [Ohm]   (rounded values, there is some weirdness going on with this also.)
The right answer should be 48 +/- 2.4 [Ohm].