Aptitude - Time and Work - Discussion
Discussion Forum : Time and Work - General Questions (Q.No. 3)
3.
A, B and C can do a piece of work in 20, 30 and 60 days respectively. In how many days can A do the work if he is assisted by B and C on every third day?
Answer: Option
Explanation:
| A's 2 day's work = |  |
1 | x 2 |  |
= | 1 | . |
| 20 | 10 |
| (A + B + C)'s 1 day's work = | |
1 | + | 1 | + | 1 | |
= | 6 | = | 1 | . |
| 20 | 30 | 60 | 60 | 10 |
| Work done in 3 days = | |
1 | + | 1 | |
= | 1 | . |
| 10 | 10 | 5 |
| Now, | 1 | work is done in 3 days. |
| 5 |
Whole work will be done in (3 x 5) = 15 days.
Discussion:
357 comments Page 24 of 36.
Varinder Singh said:
1 decade ago
Guys I want know that in last step why did the multiplied 5 and three. Please explain.
Mahesh dubey said:
1 decade ago
Its very easy.
If we cancel 6/60 = 1/10.
And 1/10 + 1/10 = 2/10 (because upper term is add and lower term is common, so when we cancel 2/10 then you got = 1/5.
If we cancel 6/60 = 1/10.
And 1/10 + 1/10 = 2/10 (because upper term is add and lower term is common, so when we cancel 2/10 then you got = 1/5.
Neha sharma said:
1 decade ago
I am Neha sharma I want to know,
How comes 6/60 = 1/10.
And 1/10 + 1/10 = 1/5.
If in 3 days work = 1/5 then how is that in 1 day =1/15.
Is it should be in 1 day 1/5 and by adding in 3 days =1/15.
Please tell me I gonne be confused.
How comes 6/60 = 1/10.
And 1/10 + 1/10 = 1/5.
If in 3 days work = 1/5 then how is that in 1 day =1/15.
Is it should be in 1 day 1/5 and by adding in 3 days =1/15.
Please tell me I gonne be confused.
Hrmridha said:
1 decade ago
A work in 3 days 3/20 part of the work.
Third day B and C work (1/30 + 1/60) = 1/20 part.
So, after 3 days work done by A, B and C = (3/20 + 1/20) = 1/5 part.
Now, 1/5 part done in 3 days.
1 part done in 5/1*3= 15 days (Ans).
Third day B and C work (1/30 + 1/60) = 1/20 part.
So, after 3 days work done by A, B and C = (3/20 + 1/20) = 1/5 part.
Now, 1/5 part done in 3 days.
1 part done in 5/1*3= 15 days (Ans).
TEJAL said:
1 decade ago
I can't understand that how the total work is calculated which is done by A.
Haphyz said:
1 decade ago
I think @Manoj made it simpler and direct. Get the portion of the job that would be completed in 3 days and then keep adding that portion in 3 days interval until you get 1.
Ggg said:
1 decade ago
A can do 1/20 of the work per day.
B can do 1/30 of the work per day.
C can do 1/60 of the work per day.
Together, they can do 1/20 + 1/30 + 1/60 of the work per day. But since B and C only help every third day, they can do, on average, 1/20 + 1/3 (1/30 + 1/60) of the work per day.
= 1/20 + 1/3 (1/30 + 1/60).
= 1/20 + 1/3 (3/60).
= 1/20 + 1/3 (1/20).
= 1/20 + 1/60.
= 4/60.
= 1/15.
So if they can do 1/15 of the work per day, they can finish the job in 15 days.
Answer: 15 days.
B can do 1/30 of the work per day.
C can do 1/60 of the work per day.
Together, they can do 1/20 + 1/30 + 1/60 of the work per day. But since B and C only help every third day, they can do, on average, 1/20 + 1/3 (1/30 + 1/60) of the work per day.
= 1/20 + 1/3 (1/30 + 1/60).
= 1/20 + 1/3 (3/60).
= 1/20 + 1/3 (1/20).
= 1/20 + 1/60.
= 4/60.
= 1/15.
So if they can do 1/15 of the work per day, they can finish the job in 15 days.
Answer: 15 days.
Lalas Hasan said:
1 decade ago
A Little Addition to @Vikas's explanation
A is working alone for two days, 3rd day he is assisted by B and C.
A's 1 day work=1/20.
A working on 2 days=2*1/20=1/10.
A+B+C working on 3rd day, so 1 day of working together = 1/20+1/30+1/60 = 6/60 = 1/10.
So total work done till 3rd day=1/10+1/10=2/10=1/5.
So if in 3 days = 1/5 of work is completed....
Total work is always 1;
So in order to make the value of RHS 1 multiply both side by 5;
Then, 3*5 days = 1/5*5 work will be completed.
= 15 days.
A is working alone for two days, 3rd day he is assisted by B and C.
A's 1 day work=1/20.
A working on 2 days=2*1/20=1/10.
A+B+C working on 3rd day, so 1 day of working together = 1/20+1/30+1/60 = 6/60 = 1/10.
So total work done till 3rd day=1/10+1/10=2/10=1/5.
So if in 3 days = 1/5 of work is completed....
Total work is always 1;
So in order to make the value of RHS 1 multiply both side by 5;
Then, 3*5 days = 1/5*5 work will be completed.
= 15 days.
Randheer said:
1 decade ago
Please anyone can explain what formula we have to use for this problems?
Amey said:
1 decade ago
Why we are multiplying 3 by 5 ?
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