a diet for a sick person must contain at least 4000 units of vitamins, 50 unit of minerals and 1400 units of calories. two foods x and y are available at a cost of rs. 4 and rs. 3 per unit respectively. one unit of food x contains 200 units of vitamins, 1 unit of minerals and 40 units of calories, whereas one unit of food y contains 100 units of vitamins, 2 units of minerals and 40 units of calories... find what combination of x and y should be used to have least cost, satisfying the requirements?