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 23 of 36.
Divyanshu Dwivedi said:
1 decade ago
It is much easier by this method :
1/20 + 1/(30*3) + 1/(60*3) = 1/x.
1/20 + 1/90 + 1/180 = 1/x.
12/180 = 1/x.
x = 15 Ans.
1/20 + 1/(30*3) + 1/(60*3) = 1/x.
1/20 + 1/90 + 1/180 = 1/x.
12/180 = 1/x.
x = 15 Ans.
Vishal grade said:
1 decade ago
A's 1 day work = 5%.
B's 1 day work = 3.33%.
C's 1 day work = 1.66%.
A, B and C' 1 day work = 5+3.3+1.6 = 10%.
On 1st 2 days total work = 5+5 = 10%.
On 3rd day total work(by all 3)=10%.
In 3 day total work done=10+10=20%.
20% work done in ---- 3 days.
100% work done in --- 15 days.
B's 1 day work = 3.33%.
C's 1 day work = 1.66%.
A, B and C' 1 day work = 5+3.3+1.6 = 10%.
On 1st 2 days total work = 5+5 = 10%.
On 3rd day total work(by all 3)=10%.
In 3 day total work done=10+10=20%.
20% work done in ---- 3 days.
100% work done in --- 15 days.
Sudha said:
1 decade ago
Is there any other simple trick to solve this?
Arun said:
1 decade ago
How to make first step?
Rajaguru said:
1 decade ago
@Manoj mass reply nice bro,
3 days = 1/5.
6 days = 2/5.
9 days = 3/5.
12 days = 4/5.
15 days = 5/5(1) == work completed.
3 days = 1/5.
6 days = 2/5.
9 days = 3/5.
12 days = 4/5.
15 days = 5/5(1) == work completed.
Shruthi 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.
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.
Eliz said:
1 decade ago
Day1: A works alone = 1/20.
Day2: Again, A works alone = 1/20.
Day3: Includes work of A, B and C = 1/20+1/30+1/60.
=>6/60.
=>1/10.
NOW, work in all 3 days = 1/20 + 1/20+ 1/10.
=>1/5.
Work in 1 day =1/(3*5).
=>1/15.
Taking reciprocal now will give us the no: of days.
i.e., 15.
Day2: Again, A works alone = 1/20.
Day3: Includes work of A, B and C = 1/20+1/30+1/60.
=>6/60.
=>1/10.
NOW, work in all 3 days = 1/20 + 1/20+ 1/10.
=>1/5.
Work in 1 day =1/(3*5).
=>1/15.
Taking reciprocal now will give us the no: of days.
i.e., 15.
Alan said:
1 decade ago
Work done by A+B+C for 1 day is 1/10.
So work done by them for 3 days should 1/10 + 1/10 + 1/10 = 3/10.
How come its just for 2 days giving 1/5.
So work done by them for 3 days should 1/10 + 1/10 + 1/10 = 3/10.
How come its just for 2 days giving 1/5.
Zyr said:
1 decade ago
1work/5days = 3 days or 1/5=3 then cross multiply to get 15.
Azam rizwan said:
1 decade ago
Why are we multiplying it by 5 in the end?
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