three equations, three unknowns

Nutrition: Amount of food A, B and C to Meet the Nutrient Requirements

Problem
A nutritionist in a hospital is arranging special diets that consist of a combination of three basic foods. It is important that the patients on this diet consume exactly 310 units of calcium, 190 units of iron, and 250 units of vitamin A each day. The amounts of these nutrients in one ounce food are given in the following table.

  Units Per Ounce
Calcium Iron Vitamin A
Food A 30 10 10
Food B 10 10 30
Food C 20 20 20

How many ounces each food must be used to satisfy the nutrient requirements exactly?

A.   6 ounces of Food A, 5 ounces of Food B and 3 ounces of Food C
B.   3 ounces of Food A, 5 ounces of Food B and 6 ounces of Food C
C.   6 ounces of Food A, 3 ounces of Food B and 5 ounces of Food C
D.   5 ounces of Food A, 3 ounces of Food B and 6 ounces of Food C

Example 04 - Simultaneous Non-Linear Equations of Three Unknowns

Problem
Solve for x, y, and z from the following system of equations.
$x(y + z) = 12$   →   Equation (1)

$y(x + z) = 6$   →   Equation (2)

$z(x + y) = 10$   →   Equation (3)
 

Example 03 - Simultaneous Non-Linear Equations of Three Unknowns

Problem
Find the value of x, y, and z from the given system of equations.
$x(x + y + z) = -36$   →   Equation (1)

$y(x + y + z) = 27$   →   Equation (2)

$z(x + y + z) = 90$   →   Equation (3)
 

System of Equations

System of Linear Equations
The number of equations should be at least the number of unknowns in order to solve the variables. System of linear equations can be solved by several methods, the most common are the following,

1. Method of substitution
2. Elimination method
3. Cramer's rule
 

Many of the scientific calculators allowed in board examinations and class room exams are capable of solving system of linear equations of up to three unknowns.
 

Example 01 - Simultaneous Non-Linear Equations of Three Unknowns

Problem
Solve for x, y, and z from the following simultaneous equations.
 

$z^x \, z^y = 100\,000$   ←   equation (1)

$(z^x)^y = 100\,000$   ←   equation (2)

$\dfrac{z^x}{z^y} = 10$   ←   equation (3)
 

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