Aptitude - Chain Rule - Discussion
Discussion Forum : 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?
Answer: Option
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.
Discussion:
14 comments Page 1 of 2.
Jefferson said:
6 years ago
@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.
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.
(1)
Hary said:
1 decade ago
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.
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.
Rajkumar said:
1 decade ago
@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.
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.
Udaya said:
1 decade ago
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.
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:
1 decade ago
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.
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.
Shobhit said:
1 decade ago
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/.
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/.
Snehal said:
1 decade ago
But if we do it like this,
36 men - 18 days.
27 men - ?.
By cross multiplication, the answer will be different.
36 men - 18 days.
27 men - ?.
By cross multiplication, the answer will be different.
Parmeshwar mathpati said:
1 decade ago
But if we do it like this,
36 men - 18 days.
27 men - ?.
By cross multiplication, the answer will be different.
36 men - 18 days.
27 men - ?.
By cross multiplication, the answer will be different.
Vinod Chavan said:
9 years ago
36 men - 18 days.
27 men - ?.
x = 36 x 18.
27.
Answer is x = 24.
27 men - ?.
x = 36 x 18.
27.
Answer is x = 24.
POORNI said:
8 years ago
How to find direct and indirect proportion? Please explain this.
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