Answer:
4 days.
Explanation:
Given:
A company can complete a certain job in 12 days.
Another company can complete the same job in 9 days,
And the third company in 18 days.
Question asked:
In how many days can three companies, if they work together, complete the job ?
Solution:
In 12 days, a company can complete = 1 job
In 1 day, a company can complete = of the job ( one - twelfth part of the job)
Similarly, another company can complete in 1 day = of the job
And the third company can complete in 1 day = of the job
Now, to find number of days they will take to complete the whole job together,
In 1 day, all the three company can complete = of the job
By taking LCM of 12, 9 and 18 we get 36 = of the job
Now, of the job is done in = 1 day
Then the 1 whole job is done in = ( by unitary method )
=
=
Therefore, three companies can complete the job in 4 days, if they work together.