
Elementary Math Fractions, Percentages, Word Problems, Equations, Inequations, Factorization, Expansion 
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September 6th, 2015, 12:52 AM  #1 
Newbie Joined: Sep 2015 From: australia Posts: 9 Thanks: 2  Maths homework
Hi, I can't get my head around this problem. Any help is appreciated. Last edited by skipjack; September 6th, 2015 at 01:11 AM. 
September 6th, 2015, 01:08 AM  #2 
Senior Member Joined: Sep 2015 From: 4th Dimension Posts: 146 Thanks: 13 Math Focus: Everything (a little bit) 
It's easy. I will give you hints. First one tells the cost for given amount. Second one, try to remember $\displaystyle f'$ is the rate of change. I hope you find it. Last edited by skipjack; September 6th, 2015 at 01:13 AM. 
September 6th, 2015, 01:17 AM  #3 
Global Moderator Joined: Dec 2006 Posts: 20,810 Thanks: 2153 
Presumably, $f'\!(v)$ denotes the rate of change of $f(v)\!$ with respect to $v$.

September 6th, 2015, 01:24 AM  #4 
Senior Member Joined: Sep 2015 From: 4th Dimension Posts: 146 Thanks: 13 Math Focus: Everything (a little bit)  I am not sure, but I feel it represents rate of change of cost when the amount is at 200 l Last edited by skipjack; September 6th, 2015 at 08:25 AM. 
September 6th, 2015, 01:34 AM  #5 
Newbie Joined: Sep 2015 From: australia Posts: 9 Thanks: 2 
a) would be for 200 litres cost 4200$? b) I'm not getting the rates of change idea Last edited by skipjack; September 6th, 2015 at 08:28 AM. 
September 6th, 2015, 04:09 AM  #6  
Senior Member Joined: Dec 2012 From: Hong Kong Posts: 853 Thanks: 311 Math Focus: Stochastic processes, statistical inference, data mining, computational linguistics  Yep. Quote:
If you plot the function on a graph, and draw a tangent at the point where x = 200, the slope of the tangent will be 0.05, which shows how fast the cost is increasing at that exact point. Last edited by skipjack; September 6th, 2015 at 08:28 AM.  
September 6th, 2015, 04:20 AM  #7  
Senior Member Joined: Sep 2015 From: 4th Dimension Posts: 146 Thanks: 13 Math Focus: Everything (a little bit)  Quote:
Last edited by skipjack; September 6th, 2015 at 08:27 AM.  
September 6th, 2015, 08:17 AM  #8 
Newbie Joined: Sep 2015 From: australia Posts: 9 Thanks: 2 
I get it now, thanks!


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