Khan/khan-exercises — Issue #10159: One step inequalities - Video doesn't explain "flipping" the inequality
Author: KhanBugz
Created: 2012-01-03 22:34:21+00:00
State: open
Labels: chrome, win7, wrong-or-unclear

Reporter: rjacobson@ymail.com

In the "one-step inequalities" video, the example problem doesn't require multiplying by a negative number. Consequently, it doesn't explain the concept that when you multiply an equation by a negative number, you need to reverse the direction of the inequality symbol. This is the only video associated with this practice exercise.

The first sample problem that I received was "Solve for x: -14x <= -20/14." This requires multiplying both sides by -1/14 to solve for x.

Since the concept of "flipping" the inequality wasn't explained in the video, I gave the wrong answer -- I solved it as "x >= -10/7," rather than the correct answer of "x <= -10/7." I only learned this concept by using the "I'd like a hint" solution, which was frustrating.

I would be good either (1) to add a video that explains the concept of "flipping" when x is negative, or (2) to ensure that x is positive for all of the practice exercises for this particular module.

(This might be explained in a subsequent video, but I haven't progressed that far. If so, you could associate that video with this practice exercise, so that it shows up in the "Stuck? Watch a video" sidebar.)

[one_step_inequalities.html?seed=32&problem=0](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/one_step_inequalities.html?seed=32&problem=0&debug)

[Answer timeline](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/one_step_inequalities.html?seed=32&problem=0&debug&activity=%5B%5D)

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