Correct Answer - Option 1 : 0.8 hours
Given :
There are 3 pipes A, B and C that are attached to an empty cistern. Pipe A and pipe B can fill the cistern in 4.8 hours and 6.4 hours respectively and pipe C can drain the filled cistern in 9.6 hours.
Calculations :
Let the total time be 't' to fill the whole cistern
Pipe A per hour work = (1/4.8) units
Pipe B per hour work = (1/6.4) units
Pipe C per hour work = (1/9.6) units
So,
⇒ (1/4.8) + (1/6.4) - (1/9.6) = 1/t (pipe C is drain pipe so taken with -ve sign)
⇒ 1/t = 50/192
⇒ t = 192/50
Time taken to fill 5/24th volume of the tank = (5/24) × (192/50)
⇒ 8/10 = 0.8 hour
∴ Option 1 will be the correct answer.