Khan/khan-exercises — Issue #11123: Dependent probability - Misleading directions
Author: KhanBugz
Created: 2012-01-13 05:04:43+00:00
State: open
Labels: firefox, win7, wrong-or-unclear

Reporter: flying_horse@cox.net

Where it says to round the answer to the nearest hundredth of a percent is misleading. The probability for the fair coins comes out .06865625. The unfair coins come out to .09375. This gives a total of .16240625 ... if you work them ALL THE WAY out to the last decimal place and then add. If you round that, you get the correct answer of 16.24% However, if you round them both to the hundredth of a percent as you are working them out, you get .0687 and .0938, which added together, give you .1625 or 16.25%, which is counted wrong. I think, if that's the way it's going to be figured, the directions should read, "Work all parts of the answer out to thousandths of a percent, and round your final answer to hundredths of a percent." Had I known that, I would have worked the steps out another place instead of working it about fifteen times, then looking in shock at the answer ... and THEN figuring out what happened.

[dependent_probability.html?seed=188&problem=0](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/dependent_probability.html?seed=188&problem=0&debug)

[Answer timeline](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/dependent_probability.html?seed=188&problem=0&debug&activity=%5B%5B%22incorrect-activity%22%2C%22%5C%2229.97%25%5C%22%22%2C718%5D%2C%5B%22incorrect-activity%22%2C%22%5C%2229.98%25%5C%22%22%2C42%5D%2C%5B%22incorrect-activity%22%2C%22%5C%2216.25%25%5C%22%22%2C384%5D%2C%5B%22hint-activity%22%2C%220%22%2C138%5D%2C%5B%22hint-activity%22%2C%220%22%2C143%5D%2C%5B%22hint-activity%22%2C%220%22%2C146%5D%2C%5B%22hint-activity%22%2C%220%22%2C151%5D%2C%5B%22hint-activity%22%2C%220%22%2C154%5D%2C%5B%22hint-activity%22%2C%220%22%2C158%5D%2C%5B%22hint-activity%22%2C%220%22%2C161%5D%2C%5B%22hint-activity%22%2C%220%22%2C169%5D%2C%5B%22hint-activity%22%2C%220%22%2C171%5D%2C%5B%22hint-activity%22%2C%220%22%2C182%5D%2C%5B%22hint-activity%22%2C%220%22%2C186%5D%2C%5B%22hint-activity%22%2C%220%22%2C188%5D%5D)

["29.97%","29.98%","16.25%"]

Mozilla/5.0 (Windows NT 6.1; WOW64; rv:9.0.1) Gecko/20100101 Firefox/9.0.1

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