Time and Work Question 2 - CAT 2025
The rate of water flow through three pipes A, B and C are in the ratio 4 : 9 : 36. An empty tank can be filled up completely by pipe A in 15 hours. If all the three pipes are used simultaneously to fill up this empty tank, the time, in minutes, required to fill up the entire tank completely is nearest to:
Step-by-Step Explanation
- Define the individual efficiencies:
The rates of water flow match the individual pipes' efficiencies directly.
- Efficiency of A = 4 units/hour
- Efficiency of B = 9 units/hour
- Efficiency of C = 36 units/hour
- Calculate the total tank capacity:
Pipe A can fill the tank completely in 15 hours.
Total Capacity = Efficiency × Time
= 4 units/hour × 15 hours
= 60 units
- Analyze the simultaneous operation:
When all three pipes run together, their combined hourly efficiency is:
Combined Efficiency = 4 + 9 + 36 = 49 units/hour
Time required = Total Capacity/Combined Efficiency
= 60/49 hours
- Convert the time to minutes:
Time in minutes = 60/49 × 60
= 3600/49
≈ 73.47 minutes
The nearest whole integer value is 73 minutes.
Correct Option: A
💡 FundaMakers Tip:
Never use fractions like 1/A + 1/B + 1/C when explicit flow or efficiency ratios are provided. Treat ratio terms directly as concrete absolute values (e.g., 4, 9, and 36 units per hour). This approach yields the total capacity instantly, keeping the final step a matter of basic long division.