46.  Pipe A can fill a tank in 5 hrs, Pipe B in 10 hrs and Pipe C in 30 hrs.If all the pipes are open in how many hours will the tank be filled?


2 hrs
2.5 hrs
3 hrs
3.5 hrs


Answer

 Option

Part filled by ( A+B+C) in 1 hr = (1/5+1/10+1/30) = 1/3 therefore all the 3 pipes together will fill the tank in 3 hrs

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47.  A water tank is 2/5th full.Pipe A can fill a tank in 10 mins and pipe B can empty it in 6 mins. If both the pipes are open,how long will it take to empty or fill the tank completely?


6 mins to empty
6 mins to fill
9 mins to empty
None of these


Answer

 Option

clearly pipe B is faster than Pipe A and so the tank will be emptied. Part to be emptied = 2/5 Part emptied by (A+B) in 1 minute = (1/6 - 1/10) = 1/15 hence 1/15 : 2/5 : :1:x or x=(2/5*1*15) = 6 mins so the tank will be emptied in 6 mins

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48.  A tape can fill a tank in 6hrs.After half the is filled 3 more similar tapes are opened.What is total time taken to fill the tank completely?


3hrs 15 minutes
3hrs 45 mins
4 hrs 15 mins
4 hrs


Answer

 Option

Time taken by 1 tape to fill half the tank = 3hrs. Part filled by the 4 tapes in 1 hr = (4*1/6) = 2/3. Remaining part = (1-1/2) = 1/2 2/3: 1/2: 1: x or x =(1/2*1*3/2) = 3/4 hrs i.e.45 minutes so total time taken 3 hrs 45 mins.

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49.  A cistern can be filled by a tape in 4 hrs while it can be emptied by another tape in 9 hrs. If both the tapes are opened simultaneously then after how much time will the cistern get filled?


4.5 hrs
5 hrs
6.5 hrs
7.2 hrs


Answer

 Option

Net part filled in 1 hr = (1/4 - 1/9) = 5/36. The cistern will be filled in 36/5 hrs i.e. 7.2 hrs

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50.  Two pipes A & B can fill a tank in 20 and 30 minutes respectively.If the both pipes are used together,then how long will it take to fill the tank?


12 mins
15 mins
25 mins
50 mins


Answer

 Option

Part filled by A in 1 minute = 1/20; Part filled by B in 1 minute = 1/30. Part filled by (A+B) in 1 minute. (A+B) = (1/20+1/30) = 1/12. Hence both the pipes can fill the tank in 12 minutes

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