I would find out how much of the job each person would do in a day. in 1 day, Sam would do 1/4 of the job, Lisa would do 1/6 of the job and Tom would do 1/2 of the Job. Then i would add each of them 1/4+1/6+1/2 . Therefore in a day, they would do 95% of the job which if we approximate, they would finish in a day.
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