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[Brink of Complexity <752357@xxxxxxxxxxxxxxxxxx>]

Public bug reported:

Binary package hint: gbrainy

A train leaves the station at 30mph. 6 hours later, a second train
leaves at 50mph. How long until the second train overtakes the first?

This Gallilean Relativity question is easy to answer in a 30mph
reference frame, where the first train is "standing still" 180mi (30mph
x 6 hrs) from the "20mph" second train (50mph - 30mph).  The answer is
clearly 9 hours (180mi / 20mph), but gbrainy thinks it's 15 hours.

gbrainy claims that the method to the answer is to multiply the speed of
the *second* train by the time, and then divide by the difference in
speed.  This, however, is backwards.  To get the true answer, we must
multiply the speed of the *first* train by the time to get the
difference in distance, and then divide by the difference in speed (the
relative speed of the second train).

To fix this bug, just change the calculation to reflect that the *first*
train needs to be multiplied by the time, not the second train. That's
it!

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: gbrainy 1.51-0ubuntu1
ProcVersionSignature: Ubuntu 2.6.35-28.49-generic-pae 2.6.35.11
Uname: Linux 2.6.35-28-generic-pae i686
NonfreeKernelModules: nvidia wl
Architecture: i386
Date: Wed Apr  6 04:52:18 2011
InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Release i386 (20101007)
PackageArchitecture: all
ProcEnviron:
 LANG=en_US.utf8
 SHELL=/bin/bash
SourcePackage: gbrainy

** Affects: gbrainy (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: apport-bug i386 maverick

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https://bugs.launchpad.net/bugs/752357

Title:
  Train question has wrong answer... and wrong explanation... and
  therefore wrong calculation built-in.