A water pump fills a tank at a constant rate of 18 liters per minute. At this rate, how many...
GMAT Problem-Solving and Data Analysis : (PS_DA) Questions
A water pump fills a tank at a constant rate of \(18\) liters per minute. At this rate, how many minutes would it take the pump to fill \(126\) liters?
- \(7\)
- \(18\)
- \(108\)
- \(126\)
7
18
108
126
1. TRANSLATE the problem information
- Given information:
- Rate = 18 liters per minute (how fast the pump works)
- Volume needed = 126 liters (how much we want to fill)
- Find: Time in minutes (how long it takes)
2. INFER which rate formula to use
- We know Rate and Volume, need to find Time
- From the rate relationships, we use: \(\mathrm{Time = Volume \div Rate}\)
- This makes sense: if you're filling faster (higher rate), it takes less time
3. SIMPLIFY by substituting and calculating
- \(\mathrm{Time = 126\ liters \div 18\ liters\ per\ minute = 7\ minutes}\)
- Check our work: \(\mathrm{7\ minutes \times 18\ liters\ per\ minute = 126\ liters}\) ✓
Answer: A (7)
Why Students Usually Falter on This Problem
Most Common Error Path:
Weak TRANSLATE skill: Students confuse which number represents what quantity in rate problems.
They might think "18 liters per minute" means it takes 18 minutes, not recognizing that this is the speed of filling. This leads them to select Choice B (18) without doing any calculation.
Second Most Common Error:
Poor INFER reasoning: Students recognize they need to do something with the numbers but choose the wrong operation.
Instead of dividing, they might subtract: \(\mathrm{126 - 18 = 108}\), thinking they need to "remove" the rate from the volume somehow. This leads them to select Choice C (108).
The Bottom Line:
Rate problems require careful attention to what each number represents. The key insight is that "liters per minute" describes how fast something happens, not how long it takes to happen.
7
18
108
126