Question

Two pipes A and B can fill a cistern in 20 minutes and 30 minutes
respectively. If these pipes are turned on alternately for 1 minute each
how long will it take to the cistern to fill?

Please answer with steps

Answer 1

Answer:

24 minutes

Step-by-step explanation:

In 2 minutes the part of the cistern filled

= 1/20 + 1/30 = 5/60

= 1/12

i.e. 1/12 of part of cistern filled in 2 min

All part of cistern will be full in = 12 X 2 = 24 minutes

Answer 2

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• As the pipes are operating alternatively, thus their 2 minutes job is = 14 + 16 = 51214 + 16 = 512 

• In the next 2 minutes the pipes can fill another 512512 part of cistern. 

• Therefore, In 4 minutes the two pipes which are operating alternatively will fill 512 + 512 = 56512 + 512 = 56Remaining part = 1 − 56 = 161 - 56 = 16 

• Pipe A can fill 1414 of the cistern in 1 minute 

• Pipe A can fill 1616 of the cistern in = 2323 min 

• Therefore, Total time taken to fill the Cistern  

• 4 + 2323 minutes.

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