Question

Marcella and Danilo went to a bookstore. Marcella bought 2 notebooks and 3 pens for $14.50. Danilo bought 1 notebook and 2 pens for $7.50. How much does 1 notebook cost?

Answer 1

equation 1: 2N+3P=14.50

equation 2: 1N +2P =7.50

multiply equation 2 by 2 so that N is same as equation 1

1N+2P=7.50 x 2 = 2N+4P = 15.00

subtract equation 1 from new equation

2N+4P = 15.00 - 2N+3P=14.50 = 1P = 0.50

 so 1 pen cost 0.50

 replace 0.50 for P in equation 1:

2N+3P=14.50 =

2N +3(0.50) = 14.50

2N +1.50 =14.50

2N = 13.00

N=13.00/2 = 6.50

notebook cost 6.50

 check:

2(6.50) + 3(0.50) = 13 +1.50 = 14.50

1(6.50) +2(0.50) =6.50 + 1.00 = 7.50

 both equations work

 Pens cost 0.50 each

 notebooks cost 6.50 each