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Question 05 (c) 

BirdBath and Beyond Incorporated is famous for its Quetzal attracting birdfeeder solution made from water, honey and canesugar.
To make their solution, both honey and a canesugar solution are poured into a 200 L mixing tank. The honey is poured in at a rate of 1 L per minute while the sugar solution is poured in at 9 L per minute. Note that 1 L of honey contains 1 kg of sugar, while the canesugar solution contains 100g of sugar per L. Unfortunately today there is a problem with the mixing tank. It was thoroughly cleaned and is initially filled with pure water, but main valve was broken and the water cannot be drained. When the mixing process is started, the honey and sugarsolutions are poured into the tank, and the excess fluid flows out of an emergency valve at 10 L per minute and onto the floor. You should assume that the solutions mix immediately and thoroughly in the tank. (c) The bird feeder solution can only be sold if there is at least 30 kg of sugar in the 200 L tank. If the flow of sugar solution and honey is switched off after 20 minutes, can the result be sold? 
Make sure you understand the problem fully: What is the question asking you to do? Are there specific conditions or constraints that you should take note of? How will you know if your answer is correct from your work only? Can you rephrase the question in your own words in a way that makes sense to you? 
If you are stuck, check the hint below. Consider it for a while. Does it give you a new idea on how to approach the problem? If so, try it! 
Hint 

Is S(20) larger than 30? 
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Solution 

Pluggin in t=20 we obtain
Remember that and hence That means that after 20 minutes there is less than 30kg of sugar in the tank. Thus the solution cannot be sold. Found a typo? Is this solution unclear? Let us know here, visit the discussion or suggest an alternative solution.

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