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Pipes and Cisterns questions

Filling and emptying tanks.

1. Pipes A and B can fill a tank in 8 and 12 hours. Both are opened for 3 hours, then A is closed. How much longer will B take to fill the tank?

  1. 4.95 hours
  2. 5.5 hours
  3. 4.5 hours
  4. 2.5 hours
Answer

C. 4.5 hours In 3 hours they fill 3 × (1/8 + 1/12). The rest (0.38 of the tank) at 1/12 per hour takes 4.5 hours.

2. A 2900 litre tank is filled by a pipe at 40 litres per minute while a drain removes 30 litres per minute. How long does it take to fill the empty tank?

  1. 290 minutes
  2. 288 minutes
  3. 289 minutes
  4. 292 minutes
Answer

A. 290 minutes Net filling = 40 − 30 = 10 L/min. Time = 2900/10 = 290 min.

3. Three pipes can fill a tank in 12, 15 and 20 hours respectively. If all three are opened together, how long will the tank take to fill?

  1. 7 hours
  2. 4 hours
  3. 5 hours
  4. 3 hours
Answer

C. 5 hours Rate = 1/12 + 1/15 + 1/20 = 1/5. Time = 5 hours.

4. A tap fills a tank in 15 hours, but a leak empties the full tank in 20 hours. With the leak, how long does the tap take to fill the tank?

  1. 66 hours
  2. 62 hours
  3. 48 hours
  4. 60 hours
Answer

D. 60 hours Net rate = 1/15 − 1/20 = 1/60. Time = 60 hours.

5. Pipe A fills a tank in 12 hours and pipe B in 24 hours. If both are opened together, how long will it take to fill the tank?

  1. 7 hours
  2. 8 hours
  3. 10 hours
  4. 6 hours
Answer

B. 8 hours Rate = 1/12 + 1/24 = 1/8. Time = 8 hours.

6. Pipes A and B can fill a tank in 10 and 15 hours. Both are opened for 2 hours, then A is closed. How much longer will B take to fill the tank?

  1. 12 hours
  2. 9 hours
  3. 10 hours
  4. 13 hours
Answer

C. 10 hours In 2 hours they fill 2 × (1/10 + 1/15). The rest (0.67 of the tank) at 1/15 per hour takes 10 hours.

7. A 500 litre tank is filled by a pipe at 70 litres per minute while a drain removes 50 litres per minute. How long does it take to fill the empty tank?

  1. 25 minutes
  2. 26 minutes
  3. 24 minutes
  4. 20 minutes
Answer

A. 25 minutes Net filling = 70 − 50 = 20 L/min. Time = 500/20 = 25 min.

8. Three pipes can fill a tank in 6, 12 and 4 hours respectively. If all three are opened together, how long will the tank take to fill?

  1. 1 hour
  2. 3 hours
  3. 4 hours
  4. 2 hours
Answer

D. 2 hours Rate = 1/6 + 1/12 + 1/4 = 1/2. Time = 2 hours.

9. A tap fills a tank in 10 hours, but a leak empties the full tank in 15 hours. With the leak, how long does the tap take to fill the tank?

  1. 29 hours
  2. 30 hours
  3. 32 hours
  4. 28 hours
Answer

B. 30 hours Net rate = 1/10 − 1/15 = 1/30. Time = 30 hours.

10. Pipe A fills a tank in 6 hours and pipe B in 12 hours. If both are opened together, how long will it take to fill the tank?

  1. 4 hours
  2. 6 hours
  3. 5 hours
  4. 3 hours
Answer

A. 4 hours Rate = 1/6 + 1/12 = 1/4. Time = 4 hours.

11. Pipes A and B can fill a tank in 12 and 18 hours. Both are opened for 3 hours, then A is closed. How much longer will B take to fill the tank?

  1. 13.13 hours
  2. 9.45 hours
  3. 11.55 hours
  4. 10.5 hours
Answer

D. 10.5 hours In 3 hours they fill 3 × (1/12 + 1/18). The rest (0.58 of the tank) at 1/18 per hour takes 10.5 hours.

12. A 1700 litre tank is filled by a pipe at 70 litres per minute while a drain removes 60 litres per minute. How long does it take to fill the empty tank?

  1. 128 minutes
  2. 204 minutes
  3. 170 minutes
  4. 213 minutes
Answer

C. 170 minutes Net filling = 70 − 60 = 10 L/min. Time = 1700/10 = 170 min.

13. Three pipes can fill a tank in 6, 8 and 24 hours respectively. If all three are opened together, how long will the tank take to fill?

  1. 4 hours
  2. 1 hour
  3. 5 hours
  4. 3 hours
Answer

D. 3 hours Rate = 1/6 + 1/8 + 1/24 = 1/3. Time = 3 hours.

14. A tap fills a tank in 8 hours, but a leak empties the full tank in 12 hours. With the leak, how long does the tap take to fill the tank?

  1. 23 hours
  2. 24 hours
  3. 25 hours
  4. 22 hours
Answer

B. 24 hours Net rate = 1/8 − 1/12 = 1/24. Time = 24 hours.

15. Pipe A fills a tank in 30 hours and pipe B in 60 hours. If both are opened together, how long will it take to fill the tank?

  1. 22 hours
  2. 18 hours
  3. 20 hours
  4. 16 hours
Answer

C. 20 hours Rate = 1/30 + 1/60 = 1/20. Time = 20 hours.

16. Pipes A and B can fill a tank in 12 and 18 hours. Both are opened for 4 hours, then A is closed. How much longer will B take to fill the tank?

  1. 7 hours
  2. 10 hours
  3. 6 hours
  4. 8 hours
Answer

D. 8 hours In 4 hours they fill 4 × (1/12 + 1/18). The rest (0.44 of the tank) at 1/18 per hour takes 8 hours.

17. A 1200 litre tank is filled by a pipe at 90 litres per minute while a drain removes 40 litres per minute. How long does it take to fill the empty tank?

  1. 23 minutes
  2. 25 minutes
  3. 24 minutes
  4. 19 minutes
Answer

C. 24 minutes Net filling = 90 − 40 = 50 L/min. Time = 1200/50 = 24 min.

18. Three pipes can fill a tank in 20, 30 and 60 hours respectively. If all three are opened together, how long will the tank take to fill?

  1. 10 hours
  2. 8 hours
  3. 12 hours
  4. 11 hours
Answer

A. 10 hours Rate = 1/20 + 1/30 + 1/60 = 1/10. Time = 10 hours.

19. A tap fills a tank in 4 hours, but a leak empties the full tank in 6 hours. With the leak, how long does the tap take to fill the tank?

  1. 13 hours
  2. 11 hours
  3. 9 hours
  4. 12 hours
Answer

D. 12 hours Net rate = 1/4 − 1/6 = 1/12. Time = 12 hours.

20. Pipe A fills a tank in 8 hours and pipe B in 24 hours. If both are opened together, how long will it take to fill the tank?

  1. 6 hours
  2. 8 hours
  3. 7 hours
  4. 5 hours
Answer

A. 6 hours Rate = 1/8 + 1/24 = 1/6. Time = 6 hours.

21. Pipes A and B can fill a tank in 15 and 25 hours. Both are opened for 3 hours, then A is closed. How much longer will B take to fill the tank?

  1. 19 hours
  2. 17 hours
  3. 13 hours
  4. 14 hours
Answer

B. 17 hours In 3 hours they fill 3 × (1/15 + 1/25). The rest (0.68 of the tank) at 1/25 per hour takes 17 hours.

22. A 1600 litre tank is filled by a pipe at 80 litres per minute while a drain removes 40 litres per minute. How long does it take to fill the empty tank?

  1. 30 minutes
  2. 41 minutes
  3. 40 minutes
  4. 39 minutes
Answer

C. 40 minutes Net filling = 80 − 40 = 40 L/min. Time = 1600/40 = 40 min.

23. Three pipes can fill a tank in 10, 12 and 15 hours respectively. If all three are opened together, how long will the tank take to fill?

  1. 4 hours
  2. 2 hours
  3. 5 hours
  4. 6 hours
Answer

A. 4 hours Rate = 1/10 + 1/12 + 1/15 = 1/4. Time = 4 hours.

24. A tap fills a tank in 20 hours, but a leak empties the full tank in 30 hours. With the leak, how long does the tap take to fill the tank?

  1. 48 hours
  2. 60 hours
  3. 54 hours
  4. 58 hours
Answer

B. 60 hours Net rate = 1/20 − 1/30 = 1/60. Time = 60 hours.

25. Pipe A fills a tank in 10 hours and pipe B in 15 hours. If both are opened together, how long will it take to fill the tank?

  1. 4 hours
  2. 6 hours
  3. 8 hours
  4. 5 hours
Answer

B. 6 hours Rate = 1/10 + 1/15 = 1/6. Time = 6 hours.

26. Pipes A and B can fill a tank in 15 and 25 hours. Both are opened for 4 hours, then A is closed. How much longer will B take to fill the tank?

  1. 14.33 hours
  2. 15.33 hours
  3. 12.9 hours
  4. 17.2 hours
Answer

A. 14.33 hours In 4 hours they fill 4 × (1/15 + 1/25). The rest (0.57 of the tank) at 1/25 per hour takes 14.33 hours.

27. A 800 litre tank is filled by a pipe at 110 litres per minute while a drain removes 90 litres per minute. How long does it take to fill the empty tank?

  1. 38 minutes
  2. 32 minutes
  3. 40 minutes
  4. 39 minutes
Answer

C. 40 minutes Net filling = 110 − 90 = 20 L/min. Time = 800/20 = 40 min.

28. A tap fills a tank in 12 hours, but a leak empties the full tank in 20 hours. With the leak, how long does the tap take to fill the tank?

  1. 28 hours
  2. 23 hours
  3. 30 hours
  4. 29 hours
Answer

C. 30 hours Net rate = 1/12 − 1/20 = 1/30. Time = 30 hours.

29. Pipe A fills a tank in 9 hours and pipe B in 18 hours. If both are opened together, how long will it take to fill the tank?

  1. 5 hours
  2. 6 hours
  3. 7 hours
  4. 8 hours
Answer

B. 6 hours Rate = 1/9 + 1/18 = 1/6. Time = 6 hours.

30. Pipes A and B can fill a tank in 20 and 30 hours. Both are opened for 2 hours, then A is closed. How much longer will B take to fill the tank?

  1. 24 hours
  2. 25 hours
  3. 19 hours
  4. 28 hours
Answer

B. 25 hours In 2 hours they fill 2 × (1/20 + 1/30). The rest (0.83 of the tank) at 1/30 per hour takes 25 hours.

31. A 1200 litre tank is filled by a pipe at 110 litres per minute while a drain removes 60 litres per minute. How long does it take to fill the empty tank?

  1. 23 minutes
  2. 19 minutes
  3. 24 minutes
  4. 18 minutes
Answer

C. 24 minutes Net filling = 110 − 60 = 50 L/min. Time = 1200/50 = 24 min.

32. A tap fills a tank in 6 hours, but a leak empties the full tank in 10 hours. With the leak, how long does the tap take to fill the tank?

  1. 13 hours
  2. 18 hours
  3. 19 hours
  4. 15 hours
Answer

D. 15 hours Net rate = 1/6 − 1/10 = 1/15. Time = 15 hours.

33. Pipe A fills a tank in 20 hours and pipe B in 30 hours. If both are opened together, how long will it take to fill the tank?

  1. 11 hours
  2. 14 hours
  3. 12 hours
  4. 9 hours
Answer

C. 12 hours Rate = 1/20 + 1/30 = 1/12. Time = 12 hours.

34. Pipes A and B can fill a tank in 12 and 18 hours. Both are opened for 2 hours, then A is closed. How much longer will B take to fill the tank?

  1. 11 hours
  2. 13 hours
  3. 12 hours
  4. 15 hours
Answer

B. 13 hours In 2 hours they fill 2 × (1/12 + 1/18). The rest (0.72 of the tank) at 1/18 per hour takes 13 hours.

35. A 1800 litre tank is filled by a pipe at 40 litres per minute while a drain removes 30 litres per minute. How long does it take to fill the empty tank?

  1. 181 minutes
  2. 162 minutes
  3. 180 minutes
  4. 225 minutes
Answer

C. 180 minutes Net filling = 40 − 30 = 10 L/min. Time = 1800/10 = 180 min.

36. Pipes A and B can fill a tank in 20 and 30 hours. Both are opened for 4 hours, then A is closed. How much longer will B take to fill the tank?

  1. 22 hours
  2. 24 hours
  3. 20 hours
  4. 21 hours
Answer

C. 20 hours In 4 hours they fill 4 × (1/20 + 1/30). The rest (0.67 of the tank) at 1/30 per hour takes 20 hours.

37. A 1000 litre tank is filled by a pipe at 60 litres per minute while a drain removes 10 litres per minute. How long does it take to fill the empty tank?

  1. 18 minutes
  2. 25 minutes
  3. 20 minutes
  4. 16 minutes
Answer

C. 20 minutes Net filling = 60 − 10 = 50 L/min. Time = 1000/50 = 20 min.

38. Pipes A and B can fill a tank in 16 and 24 hours. Both are opened for 4 hours, then A is closed. How much longer will B take to fill the tank?

  1. 14 hours
  2. 11 hours
  3. 17 hours
  4. 12 hours
Answer

A. 14 hours In 4 hours they fill 4 × (1/16 + 1/24). The rest (0.58 of the tank) at 1/24 per hour takes 14 hours.

39. A 900 litre tank is filled by a pipe at 90 litres per minute while a drain removes 80 litres per minute. How long does it take to fill the empty tank?

  1. 99 minutes
  2. 108 minutes
  3. 90 minutes
  4. 72 minutes
Answer

C. 90 minutes Net filling = 90 − 80 = 10 L/min. Time = 900/10 = 90 min.

40. Pipes A and B can fill a tank in 16 and 24 hours. Both are opened for 2 hours, then A is closed. How much longer will B take to fill the tank?

  1. 19 hours
  2. 24 hours
  3. 17 hours
  4. 18 hours
Answer

A. 19 hours In 2 hours they fill 2 × (1/16 + 1/24). The rest (0.79 of the tank) at 1/24 per hour takes 19 hours.

41. A 2100 litre tank is filled by a pipe at 40 litres per minute while a drain removes 20 litres per minute. How long does it take to fill the empty tank?

  1. 126 minutes
  2. 105 minutes
  3. 95 minutes
  4. 104 minutes
Answer

B. 105 minutes Net filling = 40 − 20 = 20 L/min. Time = 2100/20 = 105 min.

42. Pipes A and B can fill a tank in 8 and 12 hours. Both are opened for 4 hours, then A is closed. How much longer will B take to fill the tank?

  1. 2 hours
  2. 3 hours
  3. 1 hour
  4. 4 hours
Answer

A. 2 hours In 4 hours they fill 4 × (1/8 + 1/12). The rest (0.17 of the tank) at 1/12 per hour takes 2 hours.

43. A 1700 litre tank is filled by a pipe at 30 litres per minute while a drain removes 10 litres per minute. How long does it take to fill the empty tank?

  1. 85 minutes
  2. 64 minutes
  3. 94 minutes
  4. 86 minutes
Answer

A. 85 minutes Net filling = 30 − 10 = 20 L/min. Time = 1700/20 = 85 min.

44. Pipes A and B can fill a tank in 8 and 12 hours. Both are opened for 2 hours, then A is closed. How much longer will B take to fill the tank?

  1. 9 hours
  2. 7 hours
  3. 8 hours
  4. 5 hours
Answer

B. 7 hours In 2 hours they fill 2 × (1/8 + 1/12). The rest (0.58 of the tank) at 1/12 per hour takes 7 hours.

45. A 1600 litre tank is filled by a pipe at 90 litres per minute while a drain removes 40 litres per minute. How long does it take to fill the empty tank?

  1. 35 minutes
  2. 34 minutes
  3. 32 minutes
  4. 24 minutes
Answer

C. 32 minutes Net filling = 90 − 40 = 50 L/min. Time = 1600/50 = 32 min.

46. Pipes A and B can fill a tank in 6 and 9 hours. Both are opened for 2 hours, then A is closed. How much longer will B take to fill the tank?

  1. 2 hours
  2. 4 hours
  3. 6 hours
  4. 5 hours
Answer

B. 4 hours In 2 hours they fill 2 × (1/6 + 1/9). The rest (0.44 of the tank) at 1/9 per hour takes 4 hours.

47. A 2700 litre tank is filled by a pipe at 90 litres per minute while a drain removes 80 litres per minute. How long does it take to fill the empty tank?

  1. 297 minutes
  2. 272 minutes
  3. 270 minutes
  4. 338 minutes
Answer

C. 270 minutes Net filling = 90 − 80 = 10 L/min. Time = 2700/10 = 270 min.

48. Pipes A and B can fill a tank in 16 and 24 hours. Both are opened for 3 hours, then A is closed. How much longer will B take to fill the tank?

  1. 15.5 hours
  2. 16.5 hours
  3. 17.5 hours
  4. 14.5 hours
Answer

B. 16.5 hours In 3 hours they fill 3 × (1/16 + 1/24). The rest (0.69 of the tank) at 1/24 per hour takes 16.5 hours.

49. A 1000 litre tank is filled by a pipe at 90 litres per minute while a drain removes 50 litres per minute. How long does it take to fill the empty tank?

  1. 28 minutes
  2. 31 minutes
  3. 25 minutes
  4. 20 minutes
Answer

C. 25 minutes Net filling = 90 − 50 = 40 L/min. Time = 1000/40 = 25 min.

50. A 2100 litre tank is filled by a pipe at 90 litres per minute while a drain removes 80 litres per minute. How long does it take to fill the empty tank?

  1. 189 minutes
  2. 210 minutes
  3. 263 minutes
  4. 208 minutes
Answer

B. 210 minutes Net filling = 90 − 80 = 10 L/min. Time = 2100/10 = 210 min.

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