A can do a job in 15 minutes, B takes 20 minutes while C takes 30 minutes to do the same job. All three begin working together. A leaves after 2 minutes, leaving B and C to continue working together. B leaves 4 minutes after that, leaving C to finish the job. How much more time will take to finish the job?
Answers
Given:
A can do a job in 15 minutes
B takes 20 minutes
C takes 30 minutes
All three begin working together. A leaves after 2 minutes, B and C continue working together. B leaves 4 minutes hence, C finishes the job.
To find:
How much more time will be taken to finish the job?
Solution:
By LCM method-
Finding the total work by determining the LCM of 15,20 and 30, which is 60
So, efficiency( work done in 1 min) of A= 60/15= 4
Efficiency of B= 60/20 = 3
Efficiency of C= 60/30 = 2
Work done by the three in first two minutes= 9*2= 18
Work done by B and C in the next 4 minutes= 5*4= 20
So total work done till now= 18+20= 38
Work remaining= 60-38= 22
This work is to be done by C alone
So, time taken by C to complete the remaining work= 22/2 = 11 minutes
11 minutes more will be taken to finish the job by C.