Word problem please help

Question

A principal of $2100 was invested in the stock market. Some shares of World oil were bought at $7.50 per share. Some shares of Zinco Mines were bought at $3.25 per share. The total number of shares was 450. How many shares of each stock were bought?

Answer 1

We have 2 unknowns, therefore we need 2 equations to solve for this.

Let x = # of World Oil shares bought

y = # of Zinco Mines shares bought

Eq. I: x + y = 450

Eq. II: 7.50x + 3.25y = 2100

We can use either the substitution or elimination methods to solve this. Let's use the elimination method. First, multiply everything in Eq. I by 7.50

Eq. I 7.50x + 7.50y = 7.50(450)

7.50x + 7.50y = 3375

Now, subtract Eq. II from this Eq. I:

7.50x + 7.50y = 3375

-7.50x - 3.25y = -2100

0x + 4.25y = 1275

y = 1275/4.25

y = 300

Using this answer for y in Eq. I we can now solve for x:

x + y = 450

x + 300 = 450

x = 450 - 300

x = 150

Therefore, your answer is that 150 shares of World Oil and 300 shares of Zinco Mines were bought for $2100. Using these values for x and y in Eq. II and you will see that these numbers satisfy this equation also!

Hope this helps!