Aptitude - Time and Work - Discussion
Discussion Forum : Time and Work - General Questions (Q.No. 29)
29.
A and B can do a job together in 7 days. A is 1
times as efficient as B. The same job can be done by A alone in :
times as efficient as B. The same job can be done by A alone in :Answer: Option
Explanation:
| (A's 1 day's work) : (B's 1 day's work) = | 7 | : 1 = 7 : 4. |
| 4 |
Let A's and B's 1 day's work be 7x and 4x respectively.
| Then, 7x + 4x = | 1 |  11x = |
1 | x = |
1 | . |
| 7 | 7 | 77 |
 A's 1 day's work = |
 |
1 | x 7 |  |
= | 1 | . |
| 77 | 11 |
Discussion:
53 comments Page 5 of 6.
Bharathi said:
8 years ago
It's easy to understand. Thanks @Kuntal.
Yashwanth said:
8 years ago
What will be the answer for same problem with A is twice the efficiency of B?
Swapna said:
8 years ago
7+4=11......28 ,7....? 11/7*28 = 44 ans.
Padma said:
8 years ago
Why have they taken efficiency as such without converting it to number of days?
Padma said:
8 years ago
Efficiency of A:B = 7/4k : k.
No of days taken by A: B = 4k/7k = 4/7 (no of days taken = ratio of the reciprocals of the efficiency).
Let the work done in one day = 1/s.
then , work done by A in one day = 4/s.
work done by B in one day = 7/s.
work done by A+B = 1/7.
4/s + 7/s = 1/7.
11/s = 1/7.
s= 77.
Work done by A in one day = 4/s.
= 4/77.
the efficiency of A = 7/4.
Hence, work done by A in one day = 4/77 * 7/4.
= 1/11
Thus, A can do the job in 11 days.
No of days taken by A: B = 4k/7k = 4/7 (no of days taken = ratio of the reciprocals of the efficiency).
Let the work done in one day = 1/s.
then , work done by A in one day = 4/s.
work done by B in one day = 7/s.
work done by A+B = 1/7.
4/s + 7/s = 1/7.
11/s = 1/7.
s= 77.
Work done by A in one day = 4/s.
= 4/77.
the efficiency of A = 7/4.
Hence, work done by A in one day = 4/77 * 7/4.
= 1/11
Thus, A can do the job in 11 days.
(1)
Prabhu said:
8 years ago
Nice explanation @Jimmy John.
Hellani said:
8 years ago
Can you please explain me? Please.
(1)
Faisal said:
8 years ago
(A+B)'s 1 day = 1/7
And given that,
B=(4/7)A.
(A+ (4/7)A) 1 day = 1/7
(11/7) A 1 day = 1/7
11 A 1 day= 1
A's 1 day= 1/11.
Therefore, A needs 11 days alone to complete the required work.
And given that,
B=(4/7)A.
(A+ (4/7)A) 1 day = 1/7
(11/7) A 1 day = 1/7
11 A 1 day= 1
A's 1 day= 1/11.
Therefore, A needs 11 days alone to complete the required work.
(4)
Nesha said:
7 years ago
Thank you @Jimmy John.
(1)
Sourav Kalal said:
4 years ago
Here is my simple approach
------------------------------------
A=7 (A's 1 day work)
B=4 (B's 1 day work)
------------------------------------
A+B = 11 (A+B's 1 day work).
A+B can finish work in 7 days,
So, Total work = 11*7=77 unit.
A can do 7 units of work in 1 day.
for 77 unit he will take 77/7= 11 days.
(7 ----> 1,
77 ---> ?) = 77/7.
------------------------------------
A=7 (A's 1 day work)
B=4 (B's 1 day work)
------------------------------------
A+B = 11 (A+B's 1 day work).
A+B can finish work in 7 days,
So, Total work = 11*7=77 unit.
A can do 7 units of work in 1 day.
for 77 unit he will take 77/7= 11 days.
(7 ----> 1,
77 ---> ?) = 77/7.
(22)
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