A contractor hires Amitabh to complete the work, and Amitabh can do the work in 25 days. Amitabh worked for 5 days, and after that, Bindu completed it in 20 days. In how many days will Amitabh and Bindu together finish the work?
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$25/2 days$
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$25/8 days$
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$25/3 days$
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$25/4 days$
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None of these
A
Correct answer
Explanation
Amitabh completes 1/5 of work in 5 days, so his rate is 1/25 per day. Remaining 4/5 work is done by Bindu in 20 days, so her rate is (4/5)/20 = 1/25 per day. Together, their combined rate is 1/25 + 1/25 = 2/25 per day. Time to complete full work together: 1/(2/25) = 25/2 days.