Science:Math Exam Resources/Courses/MATH152/April 2022/Question B1 (b)

MATH152 April 2022

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Question B1 (b)
This is a continuation from B1 (a). (b) Find how many boxes of each type were produced. Is there more than one answer? If so, give the general solution of the mathematical problem in parametric form. Note: it is not necessary to ensure that the solution consist of positive integers.

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 hints below. Read the first one and consider it for a while. Does it give you a new idea on how to approach the problem? If so, try it! If after a while you are still stuck, go for the next hint.

Hint 1
In B1 (a), we put the augmented matrix describing the mathematical problem in a special reduced form. Does the linear system look like it has a unique or multiple solutions?

Hint 2

Checking a solution serves two purposes: helping you if, after having used all the hints, you still are stuck on the problem; or if you have solved the problem and would like to check your work. If you are stuck on a problem: Read the solution slowly and as soon as you feel you could finish the problem on your own, hide it and work on the problem. Come back later to the solution if you are stuck or if you want to check your work. If you want to check your work: Don't only focus on the answer, problems are mostly marked for the work you do, make sure you understand all the steps that were required to complete the problem and see if you made mistakes or forgot some aspects. Your goal is to check that your mental process was correct, not only the result.

Solution

Found a typo? Is this solution unclear? Let us know here. Please rate my easiness! It's quick and helps everyone guide their studies. We have the following reduced augmented matrix: $$\left[{\begin{array}{cccc|c}1&0&0&1&5\\0&0&0&0&0\\0&1&0&0&1\\0&0&1&2&4\\0&0&0&0&H-9\end{array}}\right],$$ which corresponds to the system of equations $${\begin{cases}n_{A}+n_{D}&=5\\n_{B}&=1\\n_{C}+2n_{D}&=4\end{cases}}.$$ We see that there are be multiple solutions (since there are more variables than equations), and that the system can be solved in terms of $n_{D}$, so let $t=n_{D}$. Then we have $$n_{A}=5-t{\text{ and }}n_{C}=4-2t.$$ In parametric form, $$\left[{\begin{array}{c}n_{A}\\n_{B}\\n_{C}\\n_{D}\end{array}}\right]=\left[{\begin{array}{c}5\\1\\4\\0\end{array}}\right]+t\left[{\begin{array}{c}-1\\0\\-2\\1\end{array}}\right].$$