Writing an equation
Writing the inequality
Since Christopher earns $120 for every car he sells, if x is the number of cars he sold then he earns (in dollars)
120x
Since he makes a base salary of $500 per week, then the total he earns (in dollars) each week is:
500 + 120x
He wants to make at least $1,000, then his earnings have to be 1,000 or higher, this is
1000 ≤ 500 + 120x
This is the inequality that shows this situation.
Solving the inequality
Now, we want to find the number of cars he must sell. Since x is the number cars he sold, then we want to find which values of x satisfy the inequality we found:
1000 ≤ 500 + 120x
In order to do that we must "leave x alone" one one side of the inequality and we must remember one simple rule: if we add (or substract) a number on one side of the inequality, we must do the same on the other side, and if we multiply (or divide) one side by a positive number, then we must do the same on the other side too.
1000 ≤ 500 + 120x
↓ substracting 500 both sides
1000 - 500 ≤ 120x
500 ≤ 120x
↓dividing by 120 both sides
500/120 ≤ 120x/120
4.166... ≤ x
Since 4.166... is not a possible number for cars and it has to be more than that, then he must sell at least five cars in otder to meet his goal.
Answer - Christopher must sell 5 cars or more to meet his goal