What is the cost per dozen of each type of pen?

Question

If 11 dozen roller pens and 6 dozen ball point pens coast $104. A later order of 9 dozen roller ball pen and 12 dozen ball point pens is $117. What is the cost per dozen of each type of pen?

Answer 1

r = cost of a dozen roller ball pens

b = cost of a dozen ball point pens

 

11r + 6b = 104

9r + 12b = 117

 

Solve for r and b by substitution, matrix methods, or Cramer's rule and get

 

r = $7

b = $4.50

 

Test the answers.