A can complete 50% of a job in 9 days and B can complete 25% of the job in 9 days, when working alone. If they work together, how much of the job (in %) can they complete in 9 days?

Using the unitary method, A completes 50 percent of the job in 9 days, meaning A can do the entire job in 18 days. B completes 25 percent of the job in 9 days, meaning B can do the entire job in 36 days. The total work is the least common multiple of 18 and 36, which is 36 units, making A's rate 2 units per day and B's rate 1 unit per day. Together they produce 3 units per day, so in 9 days they complete 27 units out of 36, which equals 75 percent.

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