a courier company charges $3 for every package delivered safely and pays back $5 for every package lost. If the company was paid 320 for 120 packages, how many packages did the company lose?

Answer 1

X delivered safely.
Y lost.
Eq1: x+y = 120.
Eq2: 3x - 5y = $320.
Multiply Eq1 by 5 and add the Eqs:
5x + 5y = 600
3x - 5y = 320
sum: 8x = 920
X = 115.
In Eq1, replace X with 115 and solve for Y.

Answer 2

d + L = 120

3 d + 5 L = 320

solve the system for L