JEE Main & Advanced Mathematics Linear Programming Question Bank Self Evaluation Test - Linear Programming

  • question_answer
    Every gram of wheat provides 0.1 g of proteins and 0.25g of carbohydrates. The corresponding values of rice are 0.05 g and 0.5 g respectively. Wheat costs Rs. 4 per kg and rice Rs. 6. The minimum daily requirements of proteins and carbohydrates for an average child are 50 g and 200 g respectively. Then in what quantities should wheat and rice be mixed in the daily diet to provide minimum daily requirement of proteins and carbohydrates at minimum cost

    A) 400, 200

    B) 300, 400

    C) 200, 400

    D) 400, 300   

    Correct Answer: A

    Solution :

    [a] Suppose x grams of wheat and y grams of rice are mixed in the daily diet. Since every grams of wheat provides 0.1 g of proteins and every gram of rice gives 0.05 g of proteins. Therefore, x gms of wheat and y grams of rice will provide 0.1x +0.05y g of proteins. But the minimum daily requirement of proteins is of 50g.  \[\therefore 0.1x+0.05y\ge 50\Rightarrow \frac{x}{10}+\frac{y}{20}\ge 50\]  Similarly, x grams of wheat and y grams of rice will provide 0.25x+0.5y g of carbohydrates and the minimum daily requirement of carbohydrates is of 200 g. \[\therefore 0.25x+0.5y\ge 200\Rightarrow \frac{x}{4}+\frac{y}{2}\ge 200\] Since, the quantities of wheat and rice cannot be negative. Therefore, \[x\ge 0,y\ge 0\] It is given that wheat costs 4 per kg and rice 6 per kg. So, x grams of wheat and y grams of rice will cost \[\frac{4x}{1000}+\frac{6y}{1000}\] Subject to the constraints \[\frac{x}{10}+\frac{y}{20}\ge 50,\frac{x}{4}+\frac{y}{2}\ge 200,\] and \[x\ge 0,y\ge 0\] The solution set of the linear constraints is shaded in figure. The vertices of the shaded region are \[{{A}_{2}}(800,0),P(400,200)\] and \[{{B}_{1}}(0,1000).\] The values of the objective function at these points are given in the following table.
    Point \[({{x}_{1}},{{x}_{2}})\] Value of objective function\[Z=\frac{4x}{1000}+\frac{6y}{1000}\]
    \[{{A}_{2}}(800,0)\] \[P(400,200)\] \[{{B}_{1}}(0,1000)\] \[Z=\frac{4}{1000}\times 800+\frac{8}{1000}\times 0=3.2\] \[Z=\frac{4}{1000}\times 400+\frac{6}{1000}\times 200=2.8\] \[Z=\frac{4}{1000}\times 0+\frac{6}{1000}\times 1000=6\]
    Clearly, Z is minimum for X=400 and Y=200. The minimum diet cost is 2.8.


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