Linear Inequalities

A dietitian wishes to mix together two Kinds of food so that the vitamin contents of the mixture is at least 9 units of vitamin $\mathit{A},7$ units of vitamin $\mathit{B},10$ units of vitamin C and 12 units of vitamin D. The vitamin content per Kg. of each food is shown below

	A	B	C	D
Food I	2	1	1	2
Food II	1	1	2	3

Assuming $\mathit{x}$ units of food 1 is to be mixed with $\mathit{y}$ units of food II the situation can be expressed as :