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:
359 comments Page 20 of 36.
Vipul said:
1 decade ago
Work of 1 day = 1/20+1/30+1/60= 6/60= 1/10.
It means that 1/10th part of work is done in 1 day.
(It means 10% work per day).
Now every 3rd day B And C performs -ve work i.e,
Work of every 3rd day = 1/20- 1/30-1/60 = 0/60 = 0.
Days 1 2 3 4 5 6 7 8 9 10 11 12 13 14.
Work% 10+10+0+10+10+0+10+10+0+10+10+0+10+10 = 100%.
Hence work will complete in 14 days.
Note: You can consider day 15 because in day 15 the work done will 0%.
So more correct answer will 14 days.
It means that 1/10th part of work is done in 1 day.
(It means 10% work per day).
Now every 3rd day B And C performs -ve work i.e,
Work of every 3rd day = 1/20- 1/30-1/60 = 0/60 = 0.
Days 1 2 3 4 5 6 7 8 9 10 11 12 13 14.
Work% 10+10+0+10+10+0+10+10+0+10+10+0+10+10 = 100%.
Hence work will complete in 14 days.
Note: You can consider day 15 because in day 15 the work done will 0%.
So more correct answer will 14 days.
Lallitha said:
1 decade ago
In given question, A is assisted on every 3rd days but you all doing for one 3rd day?
Can anyone explain?
Can anyone explain?
BINDU said:
1 decade ago
Here 1/5 is calculated considering ABC together but here we have to fine work done by A?
Sandhu said:
1 decade ago
Sir I can't understand the calculation of 1\20+1\30+1\60 please tell me.
Saraswati said:
1 decade ago
Another method to solve this problem:
A can do the work in 1 day = 1/20.
A can do the work in 2 days = 1/20*2 = 1/10.
B+C can do the work in 1 day = 1/30+1/60 = 1/20.
B+C can do the work in 3 days = 1/20*3 = 3/20.
A is assisted by B and C on every third day.
So that 1/20+3/20 = 1/5 (1 days work of A+3 days work of B and C).
Now, 1/5 work is done in 3 days,
Therefore whole work will be done in (3*5) = 15 days.
A can do the work in 1 day = 1/20.
A can do the work in 2 days = 1/20*2 = 1/10.
B+C can do the work in 1 day = 1/30+1/60 = 1/20.
B+C can do the work in 3 days = 1/20*3 = 3/20.
A is assisted by B and C on every third day.
So that 1/20+3/20 = 1/5 (1 days work of A+3 days work of B and C).
Now, 1/5 work is done in 3 days,
Therefore whole work will be done in (3*5) = 15 days.
Neha Sharma said:
1 decade ago
Why you are multiply 3*5? And in third step why 1/10 is taken in two times? Please exlain it?
Susi said:
1 decade ago
A's 2 days work: (1/20*2).
Answer: 1/10.
A, B, C add 1 days work. (1/20 add 1/30 add 1/60).
Answer: (110/36000).(110/2/36000/600).
Answer: (5 add 1/60).
Answer: 1(1/10).
Three days work (1/10 Add 1/10).
Answer (1/5)*3.
Answer: 16.
Answer: 1/10.
A, B, C add 1 days work. (1/20 add 1/30 add 1/60).
Answer: (110/36000).(110/2/36000/600).
Answer: (5 add 1/60).
Answer: 1(1/10).
Three days work (1/10 Add 1/10).
Answer (1/5)*3.
Answer: 16.
Aby said:
1 decade ago
Please explain the 3rd step.
Pawan choudhary said:
1 decade ago
Why the first step I don't understand please explain me?
Daniyar said:
1 decade ago
For 1st 2 days A will do work himself.
A's work in 1st 2 days:
(1/20)*2 = 1/10 or 0.1.
0.1 is 10% of total work done which is 1 or 100%.
On 3rd day B and C will assist A to do work.
A's, B's, and C's work in 3rd day:
(1/20+1/30+1/60)*1 = 1/10 or 0.1.
Again in this day three of them could do only another 10% of work out of 100% or 0.1 out of 1.
For 1st three days A, B, and C accomplished:
1/10+1/10 = 2/10, 0.2 or 20 % of total work out of 100% or 1.
To finish they need to accomplish 100-20 = 80 % or 0.8 of work remaining.
Having 20% or 3 days we need 15 (in which every 3rd day is assisted by B and C) more days (100%/20% = 5 => 5*3 = 15) to achieve total work accomplishment.
A's work in 1st 2 days:
(1/20)*2 = 1/10 or 0.1.
0.1 is 10% of total work done which is 1 or 100%.
On 3rd day B and C will assist A to do work.
A's, B's, and C's work in 3rd day:
(1/20+1/30+1/60)*1 = 1/10 or 0.1.
Again in this day three of them could do only another 10% of work out of 100% or 0.1 out of 1.
For 1st three days A, B, and C accomplished:
1/10+1/10 = 2/10, 0.2 or 20 % of total work out of 100% or 1.
To finish they need to accomplish 100-20 = 80 % or 0.8 of work remaining.
Having 20% or 3 days we need 15 (in which every 3rd day is assisted by B and C) more days (100%/20% = 5 => 5*3 = 15) to achieve total work accomplishment.
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