Linear Systems

Question

A total of 450 shares worth $2100 was invested in the stock market. Some "World Oil" shares were bought at $7.50 each. Some "Zinco Mines"  were bought at $3.25 each. How many shares of each company were bought?

Answer 1

Let W = # World Oil shares

Let Z = # Zinco Mines shares

 

The total number of shares bought was 450 so

1)  W + Z = 450

 

The total spent will be 7.5W + 3.25Z

 

2)  7.5W + 3.25Z = 2100

 

We have 2 equations with 2 unknowns.  From the

1st equation we can solve for one variable in terms

of the other and substitute that into the 2nd equation.

W + Z = 450

W = 450-Z

 

7.5(450-Z) + 3.25Z = 2100

3375 - 7.5Z + 3.25Z = 2100

-4.25Z + 3375 = 2100

-4.25Z = -1275

Z = -1275/-4.25

Z = 300

 

300 shares of Zinco Mines were purchased

W = 450-Z = 150 shares of World Oil were purchased.