Two workers' individual times: time working together

The same question, asked 4 times: 17 Jul 2023 S3*, 20 Jul 2023 S2*, 26 Jul 2023 S3*, 27 Jul 2023 S3. Every wording below, oldest first.

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Question 1
17 Jul 2023 S3
73 $Sarthak and Mohan have been assigned a work to design a room for a ceremony, Sarthak can design the entire room in 12 days, while Mohan can design the room in 15 days. In how many days will the work be completed if they work together? (Rounded off to 2 decimal places)$
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Question 2
20 Jul 2023 S2
74 $A man can finish a work in 10 days and a woman can finish it in 12 days. In how many days will the work be finished by a man and a woman, working together every day?$
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Question 3
20 Jul 2023 S2
56 $In a factory, a piece of work is completed by Raima in 15 days while Joe can finish it in 10 days. The factory manager has to complete the work as soon as possible and so he orders Joe and Raima to work together. How many days will they take to complete the work?$
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Question 4
26 Jul 2023 S3
67 $Abraham can complete a work in 9 days, while Andrew can complete the same work in 6 days. In how many days can they complete the work if they work together?$
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Question 5
27 Jul 2023 S3
69 $A can finish a job in 8 hours and B can finish the same job in 12 hours independently. If they work simultaneously, in how many hours can they do the same job?$
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Question 1