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 12 of 36.
Prabhu said:
8 years ago
Can anyone solve this?
Problem: 'A' can do a piece of in 6days, 'B' in 9days and 'C' in 12 days. In how many days will all of the together finish the work?
Problem: 'A' can do a piece of in 6days, 'B' in 9days and 'C' in 12 days. In how many days will all of the together finish the work?
Karthik said:
8 years ago
How comes 300 please explain?
Asi ganesh said:
9 years ago
Why sub (1-7/15)?
I can explain
7/15 is A, B are together work in 4 days
Then question is remaining work is nothing but left this work is total work is 1 and remaining work is is nothing but all of you know
(1-7/15)=8/15.
I can explain
7/15 is A, B are together work in 4 days
Then question is remaining work is nothing but left this work is total work is 1 and remaining work is is nothing but all of you know
(1-7/15)=8/15.
Shiva said:
9 years ago
Why sub (1-7/15)? please explain.
Jenifer said:
9 years ago
@Shubam Mishra.
Because 60 is just the value of L.C.M.
Because 60 is just the value of L.C.M.
NISHA said:
9 years ago
Why sub this (1-7/15) can you explain?
Shubham mishra said:
9 years ago
@Ankit kain.
In the last step why you take 28/60 instead of 60/28?
In the last step why you take 28/60 instead of 60/28?
Sagar said:
9 years ago
How to 300 come? Explain.
Ankit kain said:
9 years ago
Here is the perfect solution.
L.C.M- 60 (it is the lcm of 15 and 20 and here it is total work)
A's---------15 days|---EFFICIENCY-60÷15=4 (because, work= efficiency * time)
B's---------20 days|---EFFICIENCY-60÷20=3
combined efficiency of A and B =7.
work done by (A+B) in 4 days= 7 * 4=28(because work = efficiency * time).
hence ratio---------> 28/60=8/15.
L.C.M- 60 (it is the lcm of 15 and 20 and here it is total work)
A's---------15 days|---EFFICIENCY-60÷15=4 (because, work= efficiency * time)
B's---------20 days|---EFFICIENCY-60÷20=3
combined efficiency of A and B =7.
work done by (A+B) in 4 days= 7 * 4=28(because work = efficiency * time).
hence ratio---------> 28/60=8/15.
Rahul Manjhi said:
9 years ago
If A can do work in 15days then in 4days will be=4/15,
Similarly, if B can do work in 20days then 4days will be=4/20=1/5,
Therefore adding A and b together=4/15+1/5=7/15,
Now remaining work=1-7/15=8/15.
Similarly, if B can do work in 20days then 4days will be=4/20=1/5,
Therefore adding A and b together=4/15+1/5=7/15,
Now remaining work=1-7/15=8/15.
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