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 19 of 35.
Rahul said:
1 decade ago
Can you just guide me to know that how can we calculate the LCM of says 8, 24, 60/7.
RDT said:
1 decade ago
@KARTHIKEYAN and @RAHUL.
DONT CONFUSE.
A can do in 15 days.
A can do it in 1 days = 1/15.
Similarly B can do it = 1/20.
They work totally in a day.
1/15+1/20 = 35/300 = 7/60.
Work done by A and B for 4 days = 4(7/60) = 7/15.
So, Work left = Total work - Work done by A and B.
Therefore, work left = 1-(7/15) = 8/15.
This is the answer.
I hope this helps you.
DONT CONFUSE.
A can do in 15 days.
A can do it in 1 days = 1/15.
Similarly B can do it = 1/20.
They work totally in a day.
1/15+1/20 = 35/300 = 7/60.
Work done by A and B for 4 days = 4(7/60) = 7/15.
So, Work left = Total work - Work done by A and B.
Therefore, work left = 1-(7/15) = 8/15.
This is the answer.
I hope this helps you.
Shilambarasu said:
1 decade ago
I take LCM for a and b 15, 20 = 60. Now I take per day work a and b.
a = 15*4 and b = 20*3.
So both together work 60/7.
Then I less 4 day work 4*7 = 28. So 60-28 = 32.
Therefore 32/7 or 4.567. This is right or wrong please explain.
a = 15*4 and b = 20*3.
So both together work 60/7.
Then I less 4 day work 4*7 = 28. So 60-28 = 32.
Therefore 32/7 or 4.567. This is right or wrong please explain.
Prem said:
1 decade ago
7/60 = 20+15/300. But I am not understanding last step.
Ajay said:
1 decade ago
@Prem.
Always remember that while solving percentage total is 100% and similarly in ratio the total is 1/1 i.e 1.
Example : You can say that total work is done only when ratio comes in form of 1/1 , 2,2, 3,3,...... 50/50 and so on......
Answer will always come in 1/1(i.e total).
Always remember that while solving percentage total is 100% and similarly in ratio the total is 1/1 i.e 1.
Example : You can say that total work is done only when ratio comes in form of 1/1 , 2,2, 3,3,...... 50/50 and so on......
Answer will always come in 1/1(i.e total).
Sid said:
1 decade ago
LCM 15, 20 will give you 60 (the total work).
LCM of 15 and 20,
5*3 = 15.
5*4 = 20.
THEREFORE, 3*4*5 = 60.
1 day work of A = 60/15 = 4.
1 day work of B = 60/20 = 3.
1 day work of A and B together = 4 + 3 = 7 / 60.
A and B worked together for 4 days = 4 * 7/60 = 28/60 = 7 / 15.
Therefore,
Work left = Total work - Work done in 4 days by A and B together.
Work left (IN FRACTIONS) = 1 - 7/15 = (15-7)/15 = 8/15.
Thank you for giving me an opportunity.
LCM of 15 and 20,
5*3 = 15.
5*4 = 20.
THEREFORE, 3*4*5 = 60.
1 day work of A = 60/15 = 4.
1 day work of B = 60/20 = 3.
1 day work of A and B together = 4 + 3 = 7 / 60.
A and B worked together for 4 days = 4 * 7/60 = 28/60 = 7 / 15.
Therefore,
Work left = Total work - Work done in 4 days by A and B together.
Work left (IN FRACTIONS) = 1 - 7/15 = (15-7)/15 = 8/15.
Thank you for giving me an opportunity.
L raj Scope said:
1 decade ago
How to come [1/15+1/20] = 7/60?
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.
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