Need to solve the equation by graphing

Question

Penelop's Printing Press Promptly sold 5-cent pencils and 10-cent pens to the public. It sold 25 writing utensils and took in $2.00 in sales. How many pens and pencils did Penelop's Printing sell?

Answer 1

I is the number of pencils

E is the number of pens

 

We know that 25 items were sold, so:

I + E = 25

 

We also know the value was $2, or 200 cents, so:

5I + 10E = 200

 

Subtract the first formula from the second one after multiplying the second one by 5 like this:

5I + 10E = 200

-5I - 5E = -125

-->  5E = 75

So E = 15.  There were 15 pens.

 

Go back and solve the number of pencils using the first formula:

I + 15 = 25

I = 10.  So there were 10 pencils.

 

 

We can check our work using the second formula:

5I + 10E = 200

5(10) + 10(15) = 200

 

This checks out!

 

Hope this helps, Seyer!