Resistors and Potentiometers

It's simply wrong when it says resistance in a parallel configuration is:

   R_{total} = 1/R_{1} + 1/R_{2} + 1/R_{3}

The correct equation is:

   1/R_{total} = 1/R_{1} + 1/R_{2} + 1/R_{3}

or, equivalently:

   R_{total} = 1 / ( 1/R_{1} + 1/R_{2} + 1/R_{3} )

Then when the author works through the example it mysteriously changes from the incorrect version to the correct version with no word of explanation at all.

Is this really of value? I can't imagine why this has got an upvote, but I'd be happy to hear why something at this level is considered interesting.