AlgebraVery hardYears until a value is reached
Algebra practice question
A machine's value V, in dollars, t years after purchase is modelled by V(t) = 12,000 − 900t. After how many years will its value be $4,800?
Answer: 8
12,000 − 900t = 4,800 gives 900t = 7,200, so t = 8.
Common wrong answers
- If you answered 7200
- 7,200 is the total loss in value, not the number of years.
- If you answered 18.67
- 18.67 divides 16,800 by 900, adding instead of subtracting.
- If you answered 5.33
- 5.33 divides 4,800 by 900.
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