Answer:
85 - 4x < 40
12 cars
Explanation:
He starts with 85 wheels, so the inequality starts with 85.
85 -
He then subtracts 4 wheels for each car he builds.
He builds x cars, and each car uses 4 wheels, so he subtracts 4x from 85.
85 - 4x
The number of wheels he has after building x cars, is
85 - 4x
He orders more wheels when the number of wheels is less than 40.
85 - 4x < 40 <------------ This is the inequality
Now we solve the inequality for x, the number of cars.
85 - 4x < 40
Subtract 85 from both sides.
-4x < -45
Divide both sides by -4. Remember that when you multiply or divide an inequality by a negative number, the inequality sign changes direction.
-4x/(-4) > -45/(-4)
x > 11.25
Since the number of cars must be a whole number, we round up to 12.
Check:
After he builds 12 cars, he uses 4 × 12 = 48 wheels.
85 - 48 = 37
That is the highest number of wheels less than 40 that he can have before ordering ore wheels.
12 is correct.