Khan/khan-exercises — Issue #10560: Algebra challenge - precision/accuracy of rounding
Author: KhanBugz
Created: 2012-01-06 19:30:29+00:00
State: open
Labels: firefox, lion, wrong-or-unclear

Reporter: eric@gptoyz.com

Ishaan has 94% more money today than he did this time last year. If Ishaan has $561 today, how much money did he make over this past year? (Round to the nearest cent, or hundredth of a dollar.)

Let xx be the amount of money that he had last year.

x+0.94x=$561x + 0.94x = $561

1.94x=$5611.94x = $561

x=$5611.94x = \frac{$561}{1.94}

x=$289.18x = $289.18 (rounding to the nearest penny in this step)

So, he had $289.18 last year, but we want to know how much he has made over the past year!

money made over the past year=amount of money today−amount of money last year\text{money made over the past year} = \text{amount of money today} - \text{amount of money last year}

=$561−$289.18\qquad =$561-$289.18

≈$271.82\qquad \approx $271.82

So, the answer is $271.82.

these problems, should not have rounding in the middle of the solution process. The rounding should be made at the end!!!

[algebra_challenge.html?seed=75&problem=yearly-percentages-2 (percentage_word_problems_2)](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/algebra_challenge.html?seed=75&problem=yearly-percentages-2&debug)

[Answer timeline](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/algebra_challenge.html?seed=75&problem=yearly-percentages-2&debug&activity=%5B%5B%22incorrect-activity%22%2C%22%5C%22271.83%5C%22%22%2C24%5D%2C%5B%22incorrect-activity%22%2C%22%5C%22272%5C%22%22%2C7%5D%2C%5B%22hint-activity%22%2C%220%22%2C13%5D%2C%5B%22hint-activity%22%2C%220%22%2C14%5D%2C%5B%22hint-activity%22%2C%220%22%2C14%5D%2C%5B%22hint-activity%22%2C%220%22%2C14%5D%2C%5B%22hint-activity%22%2C%220%22%2C14%5D%2C%5B%22hint-activity%22%2C%220%22%2C14%5D%2C%5B%22hint-activity%22%2C%220%22%2C15%5D%2C%5B%22hint-activity%22%2C%220%22%2C15%5D%2C%5B%22hint-activity%22%2C%220%22%2C15%5D%2C%5B%22hint-activity%22%2C%220%22%2C15%5D%5D)

["271.83","272"]

Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.7; en-US; rv:1.9.2.13) Gecko/20101203 Firefox/3.6.13

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