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28 Apr 2026, 19:00
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E
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
55%
(hard)
Question Stats:
72% (02:24) correct
28%
(02:50)
wrong
based on 98
sessions
History
Date
Time
Result
Not Attempted Yet
Working alone, machines A, B, and C can complete a task in 6, 12, and 18 hours respectively. All three machines were started together to complete the task but machine A was switched off after 2 hours and machine B was also switched off after another 1 hour. Machine C completed the remaining task. If the work was started at 1200 hrs, at what time did the work get over?
A. 1630 hrs
B. 1700 hrs
C. 1730 hrs
D. 1830 hrs
E. 1930 hrs
A. 1630 hrs
B. 1700 hrs
C. 1730 hrs
D. 1830 hrs
E. 1930 hrs
28 Apr 2026, 21:47
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Take total work = 36 units (LCM of 6, 12, 18)
Rates:
A = 6 units/hr
B = 3 units/hr
C = 2 units/hr
---
First 2 hours (A + B + C):
Work done per hour = 6 + 3 + 2 = 11
In 2 hours = 22 units
---
Next 1 hour (B + C):
Work per hour = 3 + 2 = 5
Total done = 22 + 5 = 27 units
---
Remaining work = 36 − 27 = 9 units
Only C works now:
C = 2 units/hr
Time = 9 / 2 = 4.5 hours
---
Total time = 2 + 1 + 4.5 = 7.5 hours
Start time = 12:00
End time = 12:00 + 7 hr 30 min = 7:30 p.m.
---
Final Answer: 1930 hrs
---
Hope this helps.
Feel free to tag me if you want to go through it together.
– Rajdeep
Rates:
A = 6 units/hr
B = 3 units/hr
C = 2 units/hr
---
First 2 hours (A + B + C):
Work done per hour = 6 + 3 + 2 = 11
In 2 hours = 22 units
---
Next 1 hour (B + C):
Work per hour = 3 + 2 = 5
Total done = 22 + 5 = 27 units
---
Remaining work = 36 − 27 = 9 units
Only C works now:
C = 2 units/hr
Time = 9 / 2 = 4.5 hours
---
Total time = 2 + 1 + 4.5 = 7.5 hours
Start time = 12:00
End time = 12:00 + 7 hr 30 min = 7:30 p.m.
---
Final Answer: 1930 hrs
---
Hope this helps.
Feel free to tag me if you want to go through it together.
– Rajdeep
28 Apr 2026, 22:59
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Bookmarks
1/6+1/12+1/18 = 11/36 [per hour work done]
Initially they work for 2 hrs:
22/36 work is complete or 11/18 complete.
Remaining 7/18 left or 14/36 left.
Now 1 more hour of B+C work.
B+C work 1/12+1/18 = 5/36 of work.
Remaining work left now = 14-5/36 = 9/36.
C work alone now:
x(1/18) = 9/36.
x = 4.5hrs.
Total time taken from start = 2+1+4.5hrs = 7.5 hrs.
Start = 1200 hrs, End = 1930 hrs.
Answer: Option E
Initially they work for 2 hrs:
22/36 work is complete or 11/18 complete.
Remaining 7/18 left or 14/36 left.
Now 1 more hour of B+C work.
B+C work 1/12+1/18 = 5/36 of work.
Remaining work left now = 14-5/36 = 9/36.
C work alone now:
x(1/18) = 9/36.
x = 4.5hrs.
Total time taken from start = 2+1+4.5hrs = 7.5 hrs.
Start = 1200 hrs, End = 1930 hrs.
Answer: Option E
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