A can do a piece of work in 80 days. He works at it for 10 days and then B alone finishes the remaining work in 42 days. In how many days will A and B together complete the work? MCQ with Answer and Explanation

A can do a piece of work in 80 days. He works at it for 10 days and then B alone finishes the remaining work in 42 days. In how many days will A and B together complete the work?
A. 24 days
B. 35 days
C. 25 days
D. 30 days
Answer: Option D
Solution (By JKSSB Mock Tests)
A's 10-day work = 10/80 = 1/8. Remaining work = 7/8. B completes 7/8 work in 42 days, so B completes full work in 42 * (8/7) = 48 days. Combined 1-day work = 1/80 + 1/48 = (3 + 5)/240 = 8/240 = 1/30. They finish together in 30 days.

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Practice More Time and Work Questions

Question #1
A can complete a work in 19 days and B in 22 days. If they work together, the work will be completed in:
A. 10.2
B. 20.2
C. 15.2
D. 25.2

Correct Answer: Option A


Explanation:
Combined rate = 1/19 + 1/22. Required time = 10.2 days.

This question belongs to: Maths Time and Work
Question #2
A can complete a work in 21 days and B in 17 days. If they work together, the work will be completed in:
A. 19.39
B. 24.39
C. 14.39
D. 9.39

Correct Answer: Option D


Explanation:
Combined rate = 1/21 + 1/17. Required time = 9.39 days.

This question belongs to: Maths Time and Work
Question #3
A and B can do a work in 12 days, B and C in 15 days, and C and A in 20 days. How many days will A alone take to finish the work?
A. 30 days
B. 40 days
C. 20 days
D. 60 days

Correct Answer: Option A


Explanation:
Total work = LCM(12, 15, 20) = 60 units. Efficiency of (A+B) = 5, (B+C) = 4, (C+A) = 3. Summing efficiencies gives 2*(A+B+C) = 12 => Efficiency of (A+B+C) = 6 units/day. Efficiency of A = (A+B+C) - (B+C) = 6 - 4 = 2 units/day. Time taken by A alone = 60 / 2 = 30 days.

This question belongs to: Maths Time and Work