Aptitude - Time and Work - Discussion
Discussion Forum : Time and Work - General Questions (Q.No. 1)
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 :
Answer: Option
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 |
Discussion:
351 comments Page 20 of 36.
Aravind said:
1 decade ago
Why calculate the remaining work (1-7/15) ? The question ask to find the fraction left.
Tricky said:
1 decade ago
Efficiency Method:
Total 60 unit.
A = 60/15 = 4.
B = 60/20 = 3.
Total = 7/60.
In 4 days = 4*7/60 = 28/60 = 7/15.
Remain = 1-7/15 = 8/15.
Total 60 unit.
A = 60/15 = 4.
B = 60/20 = 3.
Total = 7/60.
In 4 days = 4*7/60 = 28/60 = 7/15.
Remain = 1-7/15 = 8/15.
Vaibhav said:
1 decade ago
Why 1-7/15?
The total no. of work is 1 do 1-7/15.
If there are 2 works then 2-7/15.
If 3 works then 3-7/15.
And so on.
The total no. of work is 1 do 1-7/15.
If there are 2 works then 2-7/15.
If 3 works then 3-7/15.
And so on.
Sabaneak said:
1 decade ago
If remaining work is 8/15, how many days will it take A alone to complete the work.
Sweety said:
1 decade ago
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 = (7x1) = 7.
60 4 15.
Therefore, Remaining work = (1+7) = 8.
15 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 = (7x1) = 7.
60 4 15.
Therefore, Remaining work = (1+7) = 8.
15 15.
Aravind_appu said:
1 decade ago
A = 1/15.
B = 1/20.
Together TH = A+B.
TH = (1/15+1/20).
TH/4 = (1/15+1/20).
TH = 4((35/15*20)).
TH = 7/15.
= 1-7/15 = 8/15.
B = 1/20.
Together TH = A+B.
TH = (1/15+1/20).
TH/4 = (1/15+1/20).
TH = 4((35/15*20)).
TH = 7/15.
= 1-7/15 = 8/15.
Anand said:
1 decade ago
Balance work = 8/15.
A = 1/15, B = 1/20.
Total no of days required to complete remaining work.
A = (8/15) / (1/15) = 8 days,
B = (8/15) / (1/20) = 10 2/3 days.
A = 1/15, B = 1/20.
Total no of days required to complete remaining work.
A = (8/15) / (1/15) = 8 days,
B = (8/15) / (1/20) = 10 2/3 days.
Merlin said:
1 decade ago
Can you just explain why they are subtracting the answer from 1?
Merlin said:
1 decade ago
Why do we make an assumption that the total work is 1?
Fuhar choudhury said:
1 decade ago
I don't understand the logic behind solving such problems. Like people can assume anything anywhere I mean in the first problem itself you assumed let the amount of total work be one but why can't we take 2, 3, 4,..1001, etc. This is the reason mental maths eats me up mentally.
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