Question

ABC bookstore sells one customer 12 used books and 4 new books for $120.
Another customer buys 14 used books and 2 new books for $100. How much
is one used book (u), and one new book (n)?

Answer 1

Answer:

One used book cost 5$ and a new book cost 15$

Step-by-step explanation:

$\left \{ {{12u + 4n = 120} \atop {14u + 2n = 100}} \right.$

lets multiply the second equation ×(-2)

×$\left \{ {{12u + 4n = 120} \atop {(-2)*(14u + 2n = 100)}} \right. \\\\\left \{ {{12u + 4n = 120} \atop {-28u - 4n = -200}} \right. \\\\\\\left \ {{-16u + 0n = -80} \\,\\\left \ {{16u = 80}\\,\left \ {{u = 5}$

if u = 5 then from equation 1

12*u + 4n = 120, 60 +4n = 120, 4n=120-60, n=60/4, n=15

Answer 2

Answer: u=$5, n=$15 APEX