Pipes and cisterns — Quantitative aptitude for kids

The method

Tank = LCM units — “call the tank the LCM of the hours; fillers add units each hour, leaks take them away”

1. Tank = LCM of all the hours.
2. Each pipe: tank ÷ its hours = units an hour. Fillers +, emptiers −.
3. Time = tank ÷ net units an hour.
4. One pipe alone: together rate − the other pipe’s rate.

Use it for: Water tanks, taps and leaks, and pipes-and-cisterns questions in aptitude tests.

Worked example: Pipe A fills a tank in 12 hours and pipe B fills it in 24 hours. How many hours do both pipes take together? → 8

✏️ Practice

Work it out in your head or on paper, then tap your answer — or type it and press Check. Stuck? Press “Show me how”.

🏁 Lesson 22 test

20 questions. Check each answer, then go to the next one. Get 16 or more right to pass.

🏅 Sign in with Google to earn the 🚰 Tank Filler badge when you pass — and a certificate when you finish all 10 lessons of Part 3 · Aptitude challenge. You can still take the test without signing in.

🖨️ Pipes and Cisterns Worksheet

• Worksheet set 1 (PDF)
• Worksheet set 2 (PDF)
• Worksheet set 3 (PDF)