Find the cost of one pencil and one pen.

Question

Frank and Dennis bought some pens and pencils. Frank bought 4 pens and 5 pencils, which cost him $6.71. Dennis bought 5 pens and 3 pencils, which cost him $7.12. Find the cost of one pencil and one pen.

Answer 1

4x + 5y = 6.71

5x + 3y = 7.12

 

3*(4x + 5y = 6.71)
-5*(5x + 3y = 7.12)

 

12x + 15y = 20.13

-25x - 15y = -35.60

-13x         = -15.47

-13                 -13

 

x = 1.19

 

4(1.19) + 5y = 6.71

4.76 + 5y = 6.71

           5y = 1.95

             y = 0.39

 

x = 1.19 = cost of one pen

y = 0.39 = cost of one pencil