Khan/khan-exercises — Issue #5644: Rate problems 1 - solving for time variables
Author: KhanBugz
Created: 2011-11-05 22:12:59+00:00
State: open
Labels: leopard, safari

When solving for time in these problems, your answer can vary depending on which time variable you solve for first. In this example, if you solve for time(motorcycle) first you will get a time of 210 minutes. However, if you solve for time(train) first and then substitute that into the time(train) + time(motorcycle) = 9 hr equation, you will get an answer of 209. (This is considered the correct answer.)
Even if you are solving the problem correctly, you can still get the problem "wrong" because you solved for the time variable in a different order than the answer given. If you want the user to solve with one order vs. the other, this should at least be told in the "hints." Otherwise, it becomes a game of guessing which time variable to solve for first. There doesn't seem to be this issue with the "solve for distance" questions, but I've noticed it on just about all of the "solve for time" questions I tried.

[rate_problems_1.html?seed=199&problem=2](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/rate_problems_1.html?seed=199&problem=2&debug)

["210","209"]

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