Aptitude - Chain Rule - Discussion

Discussion :: Chain Rule - General Questions (Q.No.14)

14. 

36 men can complete a piece of work in 18 days. In how many days will 27 men complete the same work?

[A]. 12
[B]. 18
[C]. 22
[D]. 24
[E]. None of these

Answer: Option D

Explanation:

Let the required number of days be x.

Less men, More days (Indirect Proportion)

27 : 36 :: 18 : x       27 x x = 36 x 18

x = 36 x 18
27

x = 24.


Robert said: (Sep 6, 2010)  
Give the explanation fully.

Snehal said: (Sep 17, 2010)  
But if we do it like this,

36 men - 18 days.

27 men - ?.

By cross multiplication, the answer will be different.

Hary said: (Dec 12, 2010)  
Snehal,.

Here we cannot cross multiply like this.

Because, No of men is inversely proportional to no of days.

So, No of men is directly proportional to 1/no of days.

We should write it as.

No of men=k/no of days.

36 = k / 18 ------- (1).

27 = k / ? ------- (2).

Dividing (1) and (2).

36/27 = ?/18.

? = 36*18/27.

No of days = 24.

Davinder said: (Dec 28, 2010)  
please give exoplanation fully.........
i am agree with snehal

Davinder said: (Dec 28, 2010)  
please give exoplanation fully.........
i am agree with snehal

Shobhit said: (Mar 9, 2011)  
36 men 1 day work = 1/18
1 men 1 day work = 1/18 *1/36
now 27 men 1 day work = 1/18 * 1/36 *27

multiply and cancel u will get 24 ...easy/.

Parmeshwar Mathpati said: (Aug 29, 2011)  
But if we do it like this,

36 men - 18 days.

27 men - ?.

By cross multiplication, the answer will be different.

Udaya said: (Nov 15, 2012)  
36 men 18 days= 1 (work)
1 man 1 day=1/36*18
=>1/648
Hence, 27 men=1/648*27=1/24 days.
1/24 is 1 day work of 27 men.
So 27 men complete the work in 24 days.

Priya said: (Sep 27, 2014)  
Let no of days be x.
36 men do work in 18 days.
27 men do work in x days.

As no of men decrease Therefore,
Days increases so,
x = 18*36/27 = 24.

Rajkumar said: (Mar 4, 2015)  
@Snehal.

Just think in normal way if it is cross multiplying the answer is 13 (APPROX) , as men decrease days should increase it is not happening. So above explanation is true.

Vinod Chavan said: (Oct 10, 2016)  
36 men - 18 days.
27 men - ?.

x = 36 x 18.
27.

Answer is x = 24.

Poorni said: (Dec 2, 2017)  
How to find direct and indirect proportion? Please explain this.

Yash said: (Dec 3, 2017)  
Why we can not do cross multiplication? please explain.

Jefferson said: (May 9, 2019)  
@Yash

Cross multiplication does not apply here.

First, You have to identify whether it's direct or indirect proportion.
In this case, it's indirect because more men take less time to complete a job compared to a few men.

Therefore we let no. of days 27men take be x
Men: days
36 : 18
27 : x.

But for indirect proportion XY=constant.
36*18 =27*x.
Hence x = 36*18/27.
Thus x=24.

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