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Believe it or not I graduated with a BSc in Computing Science, but apparently that means nothing after being out of school for a year.

The question is:

$(c+n)/(t+n)=.25$

Solve for $n$.

My attempt:

$c+n=.25(t+n)$
$c+n=.25t+.25n$
$c+.75n=.25t$
$.75n=.25t-c$
$n=4/3(.25-c)$

But when I plug in the numbers I have, that doesn't work out, so there must be a mistake in there somewhere, but I can't seem to spot it.

Help?


The numbers I've got are:

$t=3035$
$c=413$

And the answer I expect for $n$ is $461$.

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1  
In going to the last line, the $t$ disappeared! You want $n=(4/3)(0.25t-c)$. –  André Nicolas Jun 21 '11 at 1:30
    
You assumed the worst about your math skills too soon. The more one writes, the more misteaks there will be. –  André Nicolas Jun 21 '11 at 1:40
    
@user6312: Haha... but I like me steaks! I think I always always this bad, overlooking such basic mistakes. Once I screwed up the math so bad that the answer I got in the end was actually correct. –  Mark Jun 21 '11 at 1:45

2 Answers 2

up vote 3 down vote accepted

I think you just forgot the $t$ in your last step. Should be $n=4/3(0.25t-c)$.

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Oops. That was just me forgetting to type it though....that's not the only mistake, is it? Edit: Nevermind. That was the mistake. I'm an idiot :D Math works out now. –  Mark Jun 21 '11 at 1:31
    
@Mark: you're not an idiot :) We've all been there, done that... –  amWhy Jun 21 '11 at 2:27

In the last line, $t$ has disappeared.

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