Pairwise times (A+B, B+C, C+A): one worker's or all three's time

This type of question, asked 3 times: 18 Jul 2023 S3, 20 Jul 2023 S3, 27 Jul 2023 S2. All 3 questions below, oldest first.

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Question 1
18 Jul 2023 S3
60 $A and B can finish a work in 10 days, B and C can finish it in 12 days and C and A can finish in 6 days. In how many days A alone can finish the work?$
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Question 2
20 Jul 2023 S3
54 $A and B can do a project in 9 days. B and C can do it in 12 days while C and A can do it in 18 days. In how many days A, B and C all working together, can finish the project?$
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Question 3
27 Jul 2023 S2
55 $Ram and Ramesh can do a work in 12 days, Ramesh and Somesh in 15 days and Somesh and Ram in 10 days. If Ram, Ramesh and Somesh work together, in how many days will they complete the work?$
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Question 1