Machine A can complete a job in 12 hours, and Machine B can do the

Question

Machine A can complete a job in 12 hours, and Machine B can do the same job at 1/5 of the rate of Machine A. If Machine A completes 3/4 of the job and then Machine B finishes the remaining portion, what is the total amount of time taken by Machine A and Machine B?

(A) 18 hours
(B) 20 hours
(C) 24 hours
(D) 28 hours
(E) 30 hours

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SS990 · Answer

A takes 12hrs to complete a job
B's rate is 1/5 timesbA so B takes 60hrs to complete a job

Total time T= 12*(3/4) + 60*(1/4) 
t
T=24 (c)

dhart · Answer

M/c A does 3/4 of the work in 9 days
1/4 of the wrk is left for B, at 1/5th rate of A = 1/4/1/60= 15 days 
so , total 9+15 = 24 days

madsb18 · Answer

Total work = 120 Units

Mac A's rate 120/12 = 10 units per hr. Mac B's Rate = 2 units per hr.

Mac A finishes 3/4 th of work = 3/4 * (120) = 90 units in 9 hrs. Mac B finishes the rest 30 units in 15 hrs ( 2 units per hr rate)

Total Time Taken 9+ 15 = 24 hrs.

C

laborumpossimus · Answer

so i assumed work done to be 120

A efficiency is 10 as it can complete work in 12 hrs 
meanwhile efficiency of B is 1/5 of A so it is 2 
Now the question says A completes 3/4 of the job so 90 is done by A and remaining 30 is completed by b 
So 
A MACHINE 
10{ EFFICIENCY } X HOURS = 90

Time taken 9 hours

B

2 (Efficiency ) x hours = 30

time taken - 15 hours

adding A and B 
we get 24 hours 
SO c

Machine A can complete a job in 12 hours, and Machine B can do the

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Machine A can complete a job in 12 hours, and Machine B can do the

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