11.  A, B and C together can complete a piece of work in 10 days. All the three started working at it together and after 4 days A left. Then B and C together complete the work in 10 more days. A alone could complete the work in?


15 days
16 days
25 days
50 days


Answer

 Option

Work done by A, B and C in 4 days = (1/10*4) = 2/5. Remaining work =(1- 2/5) =3/5. Now, 3/5 work is done by B and C in 10 days. whole work will be done by B and C in (10*5/3) = 50/3 days. (A+B+C)'s 1 day's work = 1/10, (B+C)'s 1 day's work = 3/50. A's 1 day's work =(1/10 - 3/50) = 2/50 =1/25. therefore A alone could complete the work in 25 days.

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12.  A works twice as fast as B.If B can complete a work in 12 days independently, the number of days in which A and B can together finish the work is?


6 days
8 days
18 days
4 days


Answer

 Option

Ratio of rates of working of A and B = 2: 1.so, ratio of times taken = 1:2. therefore A's 1 day's work = 1/6; B's 1 day's work = 1/12. (A+B)'s 1 day's work = (1/6+1/12) = 3/12 = 1/4. so, A and B together can finish the work in 4 days.

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13.  A Tyre has two punctures. The first puncture alone would have made the Tyre flat in 9 minutes and the second alone would have done it in 6 minutes.If air leaks out at a constant rate, how long does it take both the punctures together to make it flat?


1 1/2 minutes
3 1/2 minutes
3 3/5 minutes
4 1/4 minutes


Answer

 Option

1 minute's work of both the punctures = (1/9+ 1/6) = 5/18. so, both the punctures will make the Tyre flat in 18/5 = 3 3/5min.

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14.  A takes twice as much time as B or thrice as much time to finish a piece of work. Working together, they can finish the work in 2 days. B can do the work alone in


4 days
6 days
8 days
12 days


Answer

 Option

Suppose A,B and C take x, x/2 and x/3 hours respectively to finish the work. Then, (1/x+ 2/x+3/x) = 1/2 = x = 12. so, B takes 6 hours to finish the work.

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15.  A man can do a piece of work in 5 days, but with the help of his son, he can do it in 3 days. In what time can the son do it alone?


6 1/2 days
7 days
7 1/2 days
8 days


Answer

 Option

Son's 1 day's work = (1/3- 1/5) = 2/15. Therefore the son alone can do the work in 15/2 = 7 1/2 days.

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