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Joanne bought 3 pens and and 2 rulers for $10.80. Alice bought 5 pens and 4 rulers for $19.20. Nick bought 2 rulers and some pens. If Nick spent $13.20, how many pens did Nick buy?

Respuesta :

Answer:

4

Step-by-step explanation:

  • Pen = p and ruler = r
  • 3p + 2r = 10.8
  • 5p + 4r= 19.2
  • get the r to cancel out
  • 5p + 4r= 19.2
  • -6p - 4r = -21.6
  • -p = -2.4
  • p = $2.40
  • now solve for r by substituting p back into the equation
  • 3p + 2r = 10.8
  • 3(2.4) + 2r = 10.8
  • 7.2 + 2r = 10.8
  • 2r = 3.6
  • r = $1.80
  • Now that we know the cost per pen and per ruler we can find out how many pens Nick bought
  • 2(1.8) = 3.6
  • 13.2 - 3.6 = $9.60 (the amount spent on pens)
  • $9.60/$2.40 = 4
  • Nick bought 4 pens

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