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:
347 comments Page 20 of 35.
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.
Mangesh said:
1 decade ago
When they not mention the quantity of work in problem in that case assume work done is 1. For e.g A can manufacture 1 chair in 15 days while B takes 20 days to manufacture 1 chair in this work done is only 1 that is to manufacture a chair but days require is different.
Akash said:
1 decade ago
Try to avoid fraction calculation.
L.C.M of(15,20) = 60.
Let total work is 60 unit.
A can do 60/15 = 4 unit/day.
B can do 60/20 = 3 unit/day.
A+B can do = 4+3 = 7 unit/day.
A+B in 4 day can do = 7*4 = 28 unit.
Total work = 60 unit.
Remaining work = 60-28 = 32 unit.
Fraction of work = (Remaining work/Total work) = 32/60 = 8/15 (ans).
L.C.M of(15,20) = 60.
Let total work is 60 unit.
A can do 60/15 = 4 unit/day.
B can do 60/20 = 3 unit/day.
A+B can do = 4+3 = 7 unit/day.
A+B in 4 day can do = 7*4 = 28 unit.
Total work = 60 unit.
Remaining work = 60-28 = 32 unit.
Fraction of work = (Remaining work/Total work) = 32/60 = 8/15 (ans).
/mat said:
1 decade ago
Why 1/15, 1/20?
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