AlgebraEasyExpression for water left in a draining tank
Algebra practice question
A tank holds 500 litres of water and drains at 20 litres per minute. Which expression gives the number of litres left after m minutes?
- A. 500 − 20mCorrect
- B. 500 + 20m
- C. 20m − 500
- D. 480m
Answer: A. 500 − 20m
Start at 500 and subtract 20 for each minute.
Why the other answers are wrong
- B. 500 + 20m
- This fills the tank instead of draining it.
- C. 20m − 500
- This starts at −500.
- D. 480m
- This multiplies by 480 each minute.
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