Latest Elitmus Aptitude Question SOLUTION: A can build a wall in 30 days. B can demolish that wall in 60 days. If A and B work on alternate days, when will the wall be completed?

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(#M40033000) ELITMUS Numerical Ability question Time and work Keep an EYE

A can build a wall in 30 days. B can demolish that wall in 60 days. If A and B work on alternate days, when will the wall be completed?

Asked In Elitmus Ankit Boae (10 years ago)

Unsolved Read Solution (13)

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Read Solution (13) :

ROHIT RAJ  (10 years ago)

117days..
A's work in a day(1st day) = 1/30
B's work in a day(2nd day)= -1/60(demolishing)
hence in 2 days, combined work= 1/30 - 1/60
=1/60
since both works alternatively, A will work in odd days and B will work in even days.
1/60 unit work is done in 2 days
58/60 unit work will be done in 2*58 days
=116 days
remaining work=1-58/60
=2/60
=1/30
next day, it will be A's turn and A will finish the remaining 1/30 work.
hence total days=116+1=117

Is this solution Helpfull? Yes (67) | No (7)  

Ankur bhardwaj  (10 years ago)

A's 1 day work=1/30
B's 1 day work=1/60
Suppose A work for x days then it is clear that B work x-1 days.
So (x/30)-(x-1)/60=1
x=59 days (A's work)
x-1=58 days(B's work)
Thus wall will be completed in 59+58=117 days

Is this solution Helpfull? Yes (22) | No (4)  

chandni mishra  (10 years ago)

A..1day work=1/30(building the wall)
B..1day work=1/60 (demonish the wall)
As,they work in alternate days..
So,in 2 days work=1/30-1/60=1/60
So,1/60 works in 2 days
1 work in 2*60days=120days..ans

Is this solution Helpfull? Yes (8) | No (18)  

vinod  (10 years ago)

here it will take 120 days as because
the net work done in 2days is (1/30-1/60)=1/60 so it will take 2*60=120 days

Is this solution Helpfull? Yes (6) | No (7)  

Samruddhi Dabir  (8 years ago)

For completing the wall, A will work one day more than B.
Let B work for n days. Then A will have to work for (n+1) days to finally complete the wall.
A's 1 day work=1/30
B's 1 day work=1/60
Thus,
(n+1)*1/30 - n*1/60 = 1
After solving, n/60 = 29/30
n = 58
A works for (n+1) = 59 days
B works for n = 58 days
Thus, Total time = 58+59 = 117 days

Is this solution Helpfull? Yes (3) | No (2)  

mayank shekhar jha  (8 years ago)

The % of working of A is 100/30=3.33
The % of working of B is 100/60=1.66
In 2 days=(3.33-1.66)=1.66
For complete the 100 % work=100/(3.33-1.66)=100/1.66=60.24*2=120 days.

Is this solution Helpfull? Yes (1) | No (1)  

utkarsh singh  (8 years ago)

59 days
not 60 days

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Shubhangi  (8 years ago)

the rate of building is double of demolishing.

day 1 work = 1
2 work = 1/2
3 work = 3/2
4 work = 1
30*4= 120

Is this solution Helpfull? Yes (1) | No (3)  

ARPIT SAXENA  (10 years ago)

ans=
1 day work of A is 100/30=3.33
2 day work of A is 6.66
1 day work of B IS 100/60= 1.75
2 day wok is 3.5
therefore 2 day work of (a+b)=6.66-3.5=3 approximately
1 day wok combined 1.5
therefore work to be completed in 100/1.5= 75 days ans

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dd  (8 years ago)

20 days :-in 20 days it will be completed

Is this solution Helpfull? Yes | No (1)  

kumari snehlata  (7 years ago)

there is a trick to solve this type of ques.
as A is building and B is destroying.
at first take LCM(30,60)= 60
then divide 60 by 30 and 60... then for A=2 and B=1
on 2nd day,, (2-1)=1
in 60(LCM) days,, 60*2= 120 is the ans.

Is this solution Helpfull? Yes | No (3)  

Vikash kumar  (7 years ago)

correct answer is 120 if u have doubt i will make above..

Is this solution Helpfull? Yes | No (2)  

Harshita  (6 years ago)

A's one day work=1/30
B's one day work=1/60
in 2 days , work done is =1/30-1/60= 1/60
in 4 days , work done is =2*(1/60)=1/30
on 5th day A will work 1/30 and complete the wall
so ans is 5 days.

Is this solution Helpfull? Yes | No (1)  

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