AlgebraEasy–MediumWriting a linear model for a decreasing quantity
Algebra practice question
A tank holds 500 litres of water and drains at a constant rate of 20 litres per minute. Which function gives the volume V(t), in litres, remaining after t minutes?
- A. V(t) = 500 − 20tCorrect
- B. V(t) = 500 + 20t
- C. V(t) = 20 − 500t
- D. V(t) = 500t − 20
Answer: A. V(t) = 500 − 20t
The tank starts at 500 and loses 20 for each minute, so after t minutes it has lost 20t: V(t) = 500 − 20t. Check: after 5 minutes, 500 − 100 = 400.
Why the other answers are wrong
- B. V(t) = 500 + 20t
- Adding 20t would mean the tank is FILLING at 20 litres per minute.
- C. V(t) = 20 − 500t
- The starting amount and the rate are swapped. The tank starts at 500, and 20 is the per-minute change.
- D. V(t) = 500t − 20
- 500t would mean the volume grows by 500 every minute. The 500 is the starting amount, not a rate.
More Algebra questions
- Easy–Medium
A line passes through the points (0, 3) and (2, 7). What is the slope of the line? - Easy–Medium
A gym charges a $25 one-time signup fee plus $15 per month. Which equation gives the total cost C, in dollars,… - Easy–Medium
If 5(x − 2) = 3x + 4, what is the value of x? - Easy–Medium
A taxi charges a $3.50 base fare plus $2.25 per mile. If a ride costs $19.25 total, how many miles was the rid… - Easy–Medium
The equation of a line is 3x + 2y = 12. What is the y-coordinate of the point where the line crosses the y-axi… - Easy–Medium
A line in the xy-plane passes through the points (1, 5) and (4, 11). What is the y-intercept of the line?
Not affiliated with the College Board. SAT is a trademark of the College Board.