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# Aptitude - Time and Work - Discussion

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"Forgiveness is a virtue of the brave."
- Indira Gandhi
1.

A can do a work in 15 days and B in 20 days. If they work on it together for 4 days, then the fraction of the work that is left is :

[A].

 1 4

[B].

 1 10

[C].

 7 15

[D].

 8 15

Explanation:

 A's 1 day's work = 1 ; 15

 B's 1 day's work = 1 ; 20

 (A + B)'s 1 day's work = 1 + 1 = 7 . 15 20 60

 (A + B)'s 4 day's work = 7 x 4 = 7 . 60 15

 Therefore, Remaining work = 1 - 7 = 8 . 15 15

 Poorni said: (Tue, Dec 28, 2010 08:46:26 AM) Why (1 - 7/15)?

 Deepa said: (Wed, Dec 29, 2010 12:56:16 AM) Can you explain how 7/60 came?

 Appu said: (Wed, Dec 29, 2010 05:23:18 AM) @Deepa (1/50+1/20) = (20+15)/300 //This get by cross multiplication. = 35/300 = 7/60. I think your doubt is clear now.

 Sundar said: (Wed, Dec 29, 2010 06:31:34 AM) @Poorni: The total work = 1; Work done by A and B in 4 days = 7/15. Therefore, the pending work = 1 - 7/15 = 0.533333333... (or) 8/15. Hope this help you. Have a nice day!

 Beer Ibrahim said: (Fri, Dec 31, 2010 01:11:35 AM) Why (1-7/15) is applied ?

 Sundar said: (Fri, Dec 31, 2010 02:53:26 AM) @Beer Ibrahim Q: Why (1-7/15) is applied ? Ans: To calculate the work remaining. Work remaining = 8/15. Note: From the above answer, we can say 15/8 days required to complete the remaining work by A and B. Hope this will help you. Have nice day!

 Mohideen said: (Sat, Jan 1, 2011 03:38:50 AM) @sundar. Good explanation.

 Pravin Hambire said: (Wed, Jan 26, 2011 05:28:07 AM) Can you explain how 7/60 came?

 Sunny Guleria said: (Sun, Jan 30, 2011 03:02:06 AM) We have to calculate the remaining work after 4 dayz ,so why we subtract 1 dayz work from 4 day work? plz clear the question.

 Prakash said: (Sun, Feb 6, 2011 04:19:02 PM) For A:- 15 days for 1 job in 1 day 1/15 (part of the one job) for B:- 20 days for 1 job in 1 day 1/20 (part of the one job) FOR BOTH IN ONE DAY:- 1/15+1/20=7/60 FOR BOTH IN 4 DAYS:- (7/60)*4=7/15(THEY HAVE DONE) THE REST PART OF THE JOB IS:- 1-(7/15)=8/15 (ANS)

 Vishwanath said: (Sun, Feb 6, 2011 06:14:22 PM) 7/60 x4 =7/15 please explain me

 Well Wisher said: (Thu, Feb 10, 2011 01:15:39 AM) @Poorni: Why 1-(7/15)? We consider the total work as 1. The amount of (work done) is 7/15. Subtract the total work by the work done we will get the amount of work to be done That is why we use 1-(7/15). Hope this help you.

 Malli said: (Thu, Feb 10, 2011 12:11:39 PM) @Prkash. Superb explaination.

 Lottie said: (Mon, Feb 14, 2011 04:37:57 AM) I was thinking 1-7/15 will be 6/15. So how did you get 8/15. Thanx.

 Analyser said: (Sat, Feb 19, 2011 02:13:57 AM) Since work done is 7/15....which is 7 parts out of 15..... So obviously total work wud be 15/15......which is 1.... Hence we subtract 7/15...from 15/15 or 1..... i.e 1-7/15.

 Vijay Kumar said: (Tue, Feb 22, 2011 12:59:46 AM) Can you explain how 7/60 came ?

 Sundar said: (Tue, Feb 22, 2011 05:52:41 AM) @Vijay Kumar 1/15 + 1/20 = ? 1/15 * 4/4 = 4/60 ok. 1/20 * 3/3 = 3/60 ok. Now, 4/60 + 3/60 = (4+3)/60 = 7/60. Thats all. I don't know how to explain more simpler than this. Hope you can understand this. Have a nice day!

 Sheelu said: (Mon, Feb 28, 2011 05:10:10 AM) 1/15+1/20=7/60 7/60*4=8/15

 Sagar said: (Fri, Mar 18, 2011 11:52:06 PM) @deepa lcm of 15 and 20 is 60 so we get 7/60 understood

 Amrinder said: (Mon, Mar 28, 2011 03:48:52 AM) 4/60 is ok 4 is no of working and 60 is hours in day cant undestand 3/60

 Rajesh Chowdary said: (Tue, Mar 29, 2011 12:33:52 PM) Explanations are good plz share any simple methods other than these

 Trupti said: (Mon, Apr 25, 2011 02:46:55 AM) 1-7/15 should be 6/15 please explaine how 8/15......

 Parthiban said: (Sat, May 14, 2011 01:03:46 AM) @Trupti 1-7/15 = (15-7)/15 = 8/15 I hope this will help you !

 Trupti said: (Mon, May 16, 2011 03:27:51 AM) Thanks Parthiban. I understood well.

 Latha said: (Mon, May 23, 2011 01:19:42 PM) Why the rest part is only 1-7/15 ?

 Anshuman said: (Thu, May 26, 2011 01:53:02 AM) Oh! Thanks I understood well.

 Vikas said: (Wed, Jun 1, 2011 12:12:31 PM) Thanks for your explanation. But it take much time. Can you tell me tricks.

 Suba said: (Wed, Jun 22, 2011 12:06:20 PM) Why we subtract with one? can you please explain.

 Crompton said: (Thu, Jun 23, 2011 06:43:20 AM) Because we know that total work = 1 so we subtract with one.

 Depl said: (Sat, Jun 25, 2011 06:28:48 AM) Oh! Thanks I understood well.

 Sak said: (Thu, Jul 7, 2011 01:02:08 AM) 1/15 * 4/4 = 4/60 ok. 1/20 * 3/3 = 3/60 ok. How do we get 4/4 and 3/3 ? Please explain.

 Mani said: (Wed, Jul 13, 2011 04:33:01 AM) Still i have confusion. How 7/60 comes?

 Honeymayee said: (Wed, Jul 20, 2011 03:52:42 PM) Power of a=p1=w/15 Power of b=p2=w/20 Work is same so p1*15=p2*20 p1/p2=4/3 Now I do not know how to proceed. ?

 Ni333 said: (Sat, Jul 23, 2011 10:13:22 PM) Thanks analyser.

 Urmm said: (Mon, Aug 1, 2011 11:57:47 PM) L.C.M. of 15 & 20 are 60 and 60/15=4 and 60/20=3 so 4+3=7 as numerator and 60 is denominator OR 1/15+1/20=[(1*20)+(1*15)]/300=(20+15)/300=35/300=7/60 35 devide by 5 and 300 devide by 5

 Swetha said: (Fri, Aug 5, 2011 04:53:09 PM) We can solve this problem by another way also..let us see.. A can do a work in 15 days B can do a work in 20 days Take LCM for 15 & 20 i.e Total work = 60 Then, A's capacity = 60/15 = 4 B's capacity = 60/20 = 3 They work together for 4 days, Then, A's capacity + B's capacity = 4 + 3 =7 AB's one day capacity = 7 since they work for 4 days, they have done 4x7 =28 work Work left = Total work - work done by AB = 60 - 28 = 32 Remaining work / total work = 32 / 60 = 8 / 15 This method will take less time to compute guys...please try it.

 Pradeepshne said: (Sat, Aug 6, 2011 12:06:02 PM) Wow really superb.

 Sangeetha said: (Sat, Aug 6, 2011 08:33:28 PM) Yes swetha your are right. Its very simple and easy method. Thank you.

 Hashir Quraishi said: (Tue, Aug 9, 2011 06:29:51 AM) Swetha you rocked.

 Gowtham said: (Tue, Aug 9, 2011 02:33:14 PM) How came remaining days?

 Kamal said: (Sat, Aug 13, 2011 09:54:58 PM) I didn't undestand last step.

 Akanksha said: (Tue, Aug 16, 2011 01:17:10 PM) (1/50+1/20) = (20+15)/300 //This get by cross multiplication. = 35/300 = 7/60. How did 300 came?

 Neha Garg said: (Mon, Sep 12, 2011 01:44:59 AM) Let total work is 1 1/15+1/20=x/4 7/60*4=x that means x=7/15 1-7/15=8/15

 Fouzia said: (Mon, Sep 12, 2011 12:35:08 PM) Fouzia. How that 7 came I can't got it?

 Sri Harsha.P said: (Sat, Sep 17, 2011 01:00:17 PM) The way said by swetha is very long process. that wastes time in the exam hall. thats not the good way to do the problem. always prepare for ashort method. Short method takes time for the first time by practice it gives u TIME MANAGEMENT. So better to practice SM.

 Ramkumar said: (Sun, Sep 18, 2011 05:38:02 PM) Nice work swetha.

 Swetha said: (Wed, Sep 28, 2011 02:28:36 PM) @Sri harsha.p It is not very long process..it is short method only.i explained every steps.,so only it looks like long process.

 Rahul said: (Sat, Oct 8, 2011 03:32:26 PM) Ok. I guess the easier way to explain this is to subtract(20days-14days)= 5 days, We have calculated for 4 days, therfore remaining is 1;)

 James said: (Mon, Oct 17, 2011 12:14:35 PM) We can solve this problem more easily by taking efficiency. Since work=efficiency *time To take efficiency take lcm of A&B.it is 60 60/15=4 60/20=3 A'efficiency=4 & B's=3 Work=4*15 or 3*20 =60 Work=60 Since a b works together for 4 days a+b effi=4+3=7 7*4=28 Total work-work done 60-28=32(work remaining) 32/60=8/15.

 Ghhhhgh said: (Sat, Oct 29, 2011 10:59:44 PM) Here it is given that A can do a piece of work in 15 days. So now we can find the A's 1 day work whicvh is =1/15.

 Santosh said: (Sat, Oct 29, 2011 11:14:51 PM) @Pravin Hambire Q. How 7/60 came ? See 1/15 +1/20 Now find the lcm of 15 and 20, it is 60. Now if you divide 60 by 15 quotient is 4. So mulitply 1/15 with 4, it will become 4/15 . Again divide 60 by 20. Quotient is 3, now multiply 1/20 with 3. It will become 3/20. Now you alredy know that lcm of 15 nd 20 is 60. So write 60 in denominator. Now add the quotient which is 3 nd 4 and write it in numerator. So finally 7/60 . Hope you got it.

 Vinod said: (Wed, Nov 2, 2011 07:57:30 AM) Any one can explain me why we using remaining work 1-7/15 please.

 Niruban said: (Wed, Nov 16, 2011 01:04:09 PM) A does the work for a day and B does it for a same day. If we add both then it should be work done for 2 days but why is it considered as one day work?

 Sunil said: (Tue, Nov 29, 2011 10:47:09 AM) How that 60 came I can't got it?

 Ram said: (Tue, Dec 6, 2011 01:21:58 PM) Hi friends.......... A can do wrk in 15 dayz ; b Can do wrk in 20 dayz; then LCM of A&B=7/60; Explain: =1/15+1/20 =[(4/4*15)+(3/3*20)] =(4/60)+(3/60) =3+4/60 =7/60 If A and B do wrk in 4 day=(7/60 *4 ) =7/15 work is 1 so=1-7/15 =15-7/15 Ans is = 8/15 Its easy for ur understanding...............

 Santhi said: (Fri, Dec 30, 2011 08:41:10 PM) Good explanation swetha.

 Bandna said: (Wed, Jan 18, 2012 10:40:52 PM) Good shweta.

 Sai Kishore said: (Thu, Jan 26, 2012 08:12:18 PM) Still I have confusion. How 7/60 comes?

 Razeena said: (Fri, Jan 27, 2012 08:06:00 PM) Hi friends, A's 1 day work=1/15; B's 1 day work=1/20 OK.Then we calculate how much A + B can do in 1 day. ie 1/15 + 1/20 ( in fraction if denominator is different first we find the l.c.m of denominator).so we calculate the l.c.m of 15 and 20 ie 60(15 and 20 is divided by 5 we get the answer 3 and 4 so we find l.c.m by multiplying 5*3*4=60).1/15*60+1/20*60=4+3/60=7/60. if A and B do work in 4 days=7/60*4=7/15 Remaining work=1-7/15 = 8/15 [ (15*1-7)/15 = 8/15 ].

 K.Nirdesh said: (Wed, Feb 1, 2012 02:02:34 PM) 1/50+1/20) = (20+15)/300 //This get by cross multiplication. = 35/300 = 7/60. why we should Division do for (20+15)/300, how did the 300 is come?

 Shro said: (Thu, Feb 16, 2012 10:51:04 AM) Thanku Prakash :).

 Rinkesh said: (Sat, Feb 18, 2012 07:32:24 AM) Very simple, 15+20=35 15*20=300 35/300=7/60 work is 1 so=1-7/15 =15-7/15 Ans is = 8/15

 Manoj said: (Thu, Mar 1, 2012 08:42:15 PM) Can you explain how did 7/60 come?

 Manoj said: (Thu, Mar 1, 2012 08:50:54 PM) 35/300=7/60 please explain it.

 Thyag said: (Sun, Mar 11, 2012 09:09:25 AM) Hi Manoj, You need to simplify big number 35/300 in to small number for further calculation. So, you need to divide one common number of both numerator and denominator. You couldn't select 2, 3 and 4 as a dividing number. But you can use 5 as a common divider. If you divide 5 in both numerator and denominator, you will get 7/60. I hope your doubt clarified.

 Anshu said: (Sat, Mar 31, 2012 11:55:29 AM) "A" can can do a work in 15 days therefore he did 1/15 of the work in a day. "B" can do the same work in 20 days therefore he did 1/20 of the work in a day. Therefore. [1/15 + 1/20]4 = [4/60 + 3/60]4. [7/60]4 = 7/15 of the work done. The total work left = 1 - 7/15 = 15 - 7/ 15 = 8/15.

 Swamy Akunoori said: (Sun, Apr 1, 2012 12:27:33 PM) Good explanation anshu.

 Esha said: (Wed, May 9, 2012 04:56:30 PM) How did 7/20 come?

 Rashmi said: (Wed, May 16, 2012 06:15:50 PM) How did you get 7/60 please answer in simple method and tell how got 7.

 Satish said: (Wed, Jun 6, 2012 01:02:21 PM) 1/15+1/20= 7/60 How ? Please explain me clearly.

 Pramesh said: (Thu, Jun 7, 2012 11:46:22 AM) @Rashmi, @Satish : 1/15 + 1/20 Now to make the denominator value equal take LCM i.e. , = (1*20) / (15*20) + (1*15) / (15*20) Now simplify these, i.e. , multiply the values i.e. , = (20/300) + (15/300). Now, both the denominator are equal, so you can add the numerator values i.e. , = (20+15) /300 = 35/300, Now simplifying this i.e. , cancelling both numerator and denominator by 5 (a common value which both will get cancel) , We get 7/60. Hope this will help you to understand the problem.

 Guhan said: (Sat, Jul 7, 2012 08:01:55 PM) @Swetha why mutiply with (A*TOTAL CAPACITY)?

 Sanjana said: (Sat, Jul 28, 2012 02:07:41 PM) Thank you sundar nice explanation

 Dipen said: (Thu, Aug 16, 2012 07:34:15 PM) How come Remaining work 1-7/15 (note:- why come 1 value )

 Shiyamala said: (Wed, Aug 29, 2012 02:05:34 PM) A=1/15;B=1/20 [A+B]=[1/15+1/20] {1/15*20/20=20/300; 1/20*15/15=15/300} =20+15/15*20 {cross multiplication} =35/300 {20+15=35;15*20=300} =7/60 7/60*4=28/60 {4*7=28} =7/15

 Ashish said: (Mon, Sep 24, 2012 12:00:21 AM) @Esha. It's not 7/20 its 7/60 and that came after addition of Both work A and B A+B= 1/15+1/20=20+15/15*20=35/300=7/60.

 Mittal said: (Mon, Oct 1, 2012 08:31:10 PM) Plzz solve this A and B can together finish a work in 30 days. They worked at it for 20 days and then B let. The remaining work was done by A alone in 20 more days. B alone can do the entire work in. (a) 48 days (b) 50 days (c) 54 days (d) 60 days.

 Sujit said: (Fri, Nov 16, 2012 06:36:37 PM) @Dipen: Probability is always .....Total chance = 1. If you say chances of wining a match is 1/2 i.e.(50%) it means chances of losing match is also 1/2 (50%)...how this losing chances 1/2 comes? It comes from subtracting wining chances from total chance that is : 1-1/2 = 1/2 Similarly in above question Remaining work = total work (1) - 4 day's work (7/15) = 8/15 Hope you get this...Have a great time :-)

 Raj said: (Sat, Mar 16, 2013 01:36:04 AM) Can anyone explain answer for the below please? A and B can together do a piece of work in 30 days. B alone can do it in 40 days. A alone can do it in ? days. For me its coming 120 days. But in TNPSC ans is 140 days. please explain.